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12 Easy Pieces (or not?)

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12 Easy Pieces (or not?) [#permalink] New post 21 Jan 2012, 05:10
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After posting some 700+ questions, I've decided to post the problems which are not that hard. Though each question below has a trap or trick so be careful when solving. I'll post OA's with detailed solutions after some discussion. Good luck.

1. There are 5 pairs of white, 3 pairs of black and 2 pairs of grey socks in a drawer. If four socks are picked at random what is the probability of getting two socks of the same color?
A. 1/5
B. 2/5
C. 3/4
D. 4/5
E. 1

Solution: 12-easy-pieces-or-not-126366.html#p1033919

2. If x is an integer and 9<x^2<99, then what is the value of maximum possible value of x minus minimum possible value of x?
A. 5
B. 6
C. 7
D. 18
E. 20

Solution: 12-easy-pieces-or-not-126366.html#p1033921

3. Fanny and Alexander are 360 miles apart and are traveling in a straight line toward each other at a constant rate of 25 mph and 65 mph respectively, how far apart will they be exactly 1.5 hours before they meet?
A. 25 miles
B. 65 miles
C. 70 miles
D. 90 miles
E. 135 miles

Solution: 12-easy-pieces-or-not-126366.html#p1033924

4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

Solution: 12-easy-pieces-or-not-126366.html#p1033925

5. The angles in a triangle are x, 3x, and 5x degrees. If a, b and c are the lengths of the sides opposite to angles x, 3x, and 5x respectively, then which of the following must be true?
I. c>a+b
II. c^2>a^2+b^2
III. c/a/b=10/6/2

A. I only
B. II only
C. III only
D. I and III only
E. II and III only

Solution: 12-easy-pieces-or-not-126366.html#p1033930

6. Anna has 10 marbles: 5 red, 2 blue, 2 green and 1 yellow. She wants to arrange all of them in a row so that no two adjacent marbles are of the same color and the first and the last marbles are of different colors. How many different arrangements are possible?
A. 30
B. 60
C. 120
D. 240
E. 480

Solution: 12-easy-pieces-or-not-126366.html#p1033932

7. After 2/9 of the numbers in a data set A were observed, it turned out that 3/4 of those numbers were non-negative. What fraction of the remaining numbers in set A must be negative so that the total ratio of negative numbers to non-negative numbers be 2 to 1?
A. 11/14
B. 13/18
C. 4/7
D. 3/7
E. 3/14

Solution: 12-easy-pieces-or-not-126366.html#p1033933

8. There are 15 black chips and 5 white chips in a jar. What is the least number of chips we should pick to guarantee that we have 2 chips of the same color?
A. 3
B. 5
C. 6
D. 16
E. 19

Solution: 12-easy-pieces-or-not-126366.html#p1033935

9. Julie is putting M marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of M?
A. 22
B. 30
C. 38
D. 46
E. 54

Solution: 12-easy-pieces-or-not-126366.html#p1033936

10. If n is an integer and \frac{1}{10^{n+1}}<0.00737<\frac{1}{10^n}, then what is the value of n?
A. 1
B. 2
C. 3
D. 4
E. 5

Solution: 12-easy-pieces-or-not-126366.html#p1033938

11. The numbers {1, 3, 6, 7, 7, 7} are used to form three 2-digit numbers. If the sum of these three numbers is a prime number p, what is the largest possible value of p?
A. 97
B. 151
C. 209
D. 211
E. 219

Solution: 12-easy-pieces-or-not-126366-20.html#p1033939

12. If {-\frac{1}{3}}\leq{x}\leq{-\frac{1}{5}} and {-\frac{1}{2}}\leq{y}\leq{-\frac{1}{4}}, what is the least value of x^2*y possible?
A. -1/100
B. -1/50
C. -1/36
D. -1/18
E. -1/6

Solution: 12-easy-pieces-or-not-126366-20.html#p1033949
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Re: 12 Easy Pieces (or not?) [#permalink] New post 29 Apr 2013, 10:44
Q10.
For n = 1:
1/10^(n+1) = 1/10^2 = 0.01
1/10^n = 1/10^1 = 0.1

0.01 < 0.007 < 0.1 FALSE. 0.01 > 0.007

For n = 2:
1/10^(n+1) = 1/10^3 = 0.001
1/10^n = 1/10^2 = 0.01

0.001 < 0.007 < 0.01
Hence Ans B

For n = 3:
1/10^(n+1) = 1/10^4 = 0.0001
1/10^n = 1/10^3 = 0.001

0.0001 < 0.007 < 0.001 FALSE. 0.007 > 0.001
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Re: 12 Easy Pieces (or not?) [#permalink] New post 29 Apr 2013, 10:50
Q11.
Best strategy is to check answer choices. As we need to find the largest possible, good idea to start from the largest number.
Lets start with E. 219
only way to reach 219 is to have 71, 73 and 76 which total 220 (Not a prime number)

D. 211 (77 + 71 + 63) = 211 and 211 is prime
hence ans D
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Re: 12 Easy Pieces (or not?) [#permalink] New post 29 Apr 2013, 10:58
Q12. -1/3 <= x <= -1/5 and -1/2 <= y <= -1/4
we need to find minimum value of x^2 *y
x^2 ranges from 1/9 to 1/25

x^2 * y ranges from 1/9 * -1/2 = -1/18 (approx -0.06) TO 1/25 * -1/4 = -1/100 (approx -0.01)

Ans D
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Re: 12 Easy Pieces (or not?) [#permalink] New post 01 May 2013, 22:23
Bunuel wrote:
4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

To get max value of y-x take max value of y and min value of x: 9-(-3)=12;
To get min value of y-x take min value of y and max value of x: -7-(5)=-12;

Hence, the range of all possible values of y-x is -12<y-x<12.

Answer: D.


Those values of x and y you had considered would be right if there was an <= symbol at all the places where there are inequality signs. But, provided there is no = symbol along with < and >, then won't the range be -10 to +10? Please explain!
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Re: 12 Easy Pieces (or not?) [#permalink] New post 02 May 2013, 02:13
Expert's post
sharmila79 wrote:
Bunuel wrote:
4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

To get max value of y-x take max value of y and min value of x: 9-(-3)=12;
To get min value of y-x take min value of y and max value of x: -7-(5)=-12;

Hence, the range of all possible values of y-x is -12<y-x<12.

Answer: D.


Those values of x and y you had considered would be right if there was an <= symbol at all the places where there are inequality signs. But, provided there is no = symbol along with < and >, then won't the range be -10 to +10? Please explain!


If y=8.9 and x=-2.9, then y-x=11.8.
If y=-6.9 and x=4.9, then y-x=-11.8.

So, your range (-10 , 10) is clearly wrong.

Consider the following approach, we have -3<x<5 and -7<y<9,

Add y<9 and -3<x --> y-3<9+x --> y-x<12;
Add -7<y and x<5 --> -7+x<y+5 --> -12<y-x;

So, we have that -12<y-x<12.

Hope it's clear.
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Re: 12 Easy Pieces (or not?) [#permalink] New post 16 May 2013, 16:59
Thanks Bunuel for such good quality questions.
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Re: 12 Easy Pieces (or not?) [#permalink] New post 13 Jun 2013, 04:44
Bunuel wrote:
4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

To get max value of y-x take max value of y and min value of x: 9-(-3)=12;
To get min value of y-x take min value of y and max value of x: -7-(5)=-12;

Hence, the range of all possible values of y-x is -12<y-x<12.

Answer: D.


Since, the question mentions -3<x<5 and -7<y<9 and not -3<=x<=5 and -7<=y<=9, i thought that x values are not inclusive -3 and 5; similarly y values are not inclusie -7 and 9. Is my thought correct?
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Re: 12 Easy Pieces (or not?) [#permalink] New post 13 Jun 2013, 04:57
Expert's post
mamathak wrote:
Bunuel wrote:
4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

To get max value of y-x take max value of y and min value of x: 9-(-3)=12;
To get min value of y-x take min value of y and max value of x: -7-(5)=-12;

Hence, the range of all possible values of y-x is -12<y-x<12.

Answer: D.


Since, the question mentions -3<x<5 and -7<y<9 and not -3<=x<=5 and -7<=y<=9, i thought that x values are not inclusive -3 and 5; similarly y values are not inclusie -7 and 9. Is my thought correct?


Yes, your understanding is correct.
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Re: 12 Easy Pieces (or not?) [#permalink] New post 06 Jul 2013, 10:10
Bunuel wrote:
7. After 2/9 of the numbers in a data set A were observed, it turned out that 3/4 of those numbers were non-negative. What fraction of the remaining numbers in set A must be negative so that the total ratio of negative numbers to non-negative numbers be 2 to 1?
A. 11/14
B. 13/18
C. 4/7
D. 3/7
E. 3/14

If choose variable for set A there will be too many fractions to manipulate with, so pick some smart #: let set A contain 18 numbers.

"2/9 of the numbers in a data set A were observed" --> 4 observed and 18-4=14 numbers left to observe;
"3/4 of those numbers were non-negative" --> 3 non-negative and 1 negative;
Ratio of negative numbers to non-negative numbers to be 2 to 1 there should be total of 18*2/3=12 negative numbers, so in not yet observed part there should be 12-1=11 negative numbers. Thus 11/14 of the remaining numbers in set A must be negative.

Answer: A.



hey, here's my approach and i found this to be more simplified,

otal
we have 2/9 our first fraction as 2, 9 are co primes take its multiple 18 as our total kit.

2/9 = 4 of which 3 are NN and 1 is Negative, rest we have 14 of 18.
given ration of Non negative to negative is 1: 2 , 3 parts are 18 and this implies 2 parts are 12
but we already have one negative in first 4 so, we need another 11/18
done :)
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Re: 12 Easy Pieces (or not?) [#permalink] New post 06 Jul 2013, 21:12
For #7. How can we assume there is no 0 in set A? It just says numbers (either negative or non negative)
0 is neither. So I used 0 too and got the wrong answer.

Thanks
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Re: 12 Easy Pieces (or not?) [#permalink] New post 06 Jul 2013, 23:54
Expert's post
jjack0310 wrote:
For #7. How can we assume there is no 0 in set A? It just says numbers (either negative or non negative)
0 is neither. So I used 0 too and got the wrong answer.

Thanks


Please read the solution again: 12-easy-pieces-or-not-126366.html#p1033933 Pay attention to the term "non-negative" there (0 and positive) and you'll notice that no assumtion was made.
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Re: 12 Easy Pieces (or not?) [#permalink] New post 07 Jul 2013, 11:59
Bunuel wrote:
9. Julie is putting M marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of M?
A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then M=7k+3. The only answer choice which is multiple of 7 plus 3 is 38=35+3.

Answer: C.


Sorry, this may be a silly thing to ask, I don't understand the problem.
What exactly is it asking?

Can someone please explain?

I get that it is asking how many marbles does Julie have. Here is what I am understanding:

Basically there are marbles with seven different colors. Out of which blue, white and red always stay in that order since these three form a pattern. The rest of the four marbles of different colors can be in any order. But the 8th marble will always be blue followed by white and followed by white.
Is this thinking/approach correct??

If yes, where does 38 come from and if it is not correct, please tell me what's wrong.

Thanks
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Re: 12 Easy Pieces (or not?) [#permalink] New post 07 Jul 2013, 12:10
Expert's post
jjack0310 wrote:
Bunuel wrote:
9. Julie is putting M marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of M?
A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then M=7k+3. The only answer choice which is multiple of 7 plus 3 is 38=35+3.

Answer: C.


Sorry, this may be a silly thing to ask, I don't understand the problem.
What exactly is it asking?

Can someone please explain?

I get that it is asking how many marbles does Julie have. Here is what I am understanding:

Basically there are marbles with seven different colors. Out of which blue, white and red always stay in that order since these three form a pattern. The rest of the four marbles of different colors can be in any order. But the 8th marble will always be blue followed by white and followed by white.
Is this thinking/approach correct??

If yes, where does 38 come from and if it is not correct, please tell me what's wrong.

Thanks


No, that's not correct.

The question asks to determine how many marbles Julie has.

The pattern is always the same {blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}...

At some point Julie does not have enough marbles to end the pattern and the row ends with a red marble: {blue, white, red}.

For example, it could happen if she had 7+3=10 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red}

Or 7*2+3=17 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}

Or: 7*3+3=24 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}

As you can see the number of marbles is always a multiple of 7 plus 3.

The only answer choice which is multiple of 7 plus 3 is 38 = 7*5+3:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}.

Hope it's clear.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: 12 Easy Pieces (or not?) [#permalink] New post 07 Jul 2013, 12:49
Bunuel wrote:
jjack0310 wrote:
Bunuel wrote:
9. Julie is putting M marbles in a row in a repeating pattern: blue, white, red, green, black, yellow, pink. If the row begins with blue marble and ends with red marble, then which of the following could be the value of M?
A. 22
B. 30
C. 38
D. 46
E. 54

There are total of 7 different color marbles in a pattern. Now, as the row begins with blue marble and ends with red marble (so ends with 3rd marble in a pattern) then M=7k+3. The only answer choice which is multiple of 7 plus 3 is 38=35+3.

Answer: C.


Sorry, this may be a silly thing to ask, I don't understand the problem.
What exactly is it asking?

Can someone please explain?

I get that it is asking how many marbles does Julie have. Here is what I am understanding:

Basically there are marbles with seven different colors. Out of which blue, white and red always stay in that order since these three form a pattern. The rest of the four marbles of different colors can be in any order. But the 8th marble will always be blue followed by white and followed by white.
Is this thinking/approach correct??

If yes, where does 38 come from and if it is not correct, please tell me what's wrong.

Thanks


No, that's not correct.

The question asks to determine how many marbles Julie has.

The pattern is always the same {blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}...

At some point Julie does not have enough marbles to end the pattern and the row ends with a red marble: {blue, white, red}.

For example, it could happen if she had 7+3=10 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red}

Or 7*2+3=17 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}

Or: 7*3+3=24 marbles:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}

As you can see the number of marbles is always a multiple of 7 plus 3.

The only answer choice which is multiple of 7 plus 3 is 38 = 7*5+3:
{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red, green, black, yellow, pink}{blue, white, red}.

Hope it's clear.


I wasn't reading the problem correct. The question says the Row beings with blue and ends white.

I thought it said the pattern begins with blue and ends with white. --- The pattern.
But it says the row begins with blue and ends with white.

I really need to pay attention to the actual wordings of the question.
Thanks.
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Re: 12 Easy Pieces (or not?) [#permalink] New post 08 Jul 2013, 23:41
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Re: 12 Easy Pieces (or not?) [#permalink] New post 24 Jul 2013, 10:18
I think answer should change if we skip to mention "at least" in the question :

If four socks are picked at random what is the probability of getting two socks of the same color?

If four socks are picked at random what is the probability of getting (at least) two socks of the same color?
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Re: 12 Easy Pieces (or not?) [#permalink] New post 17 Sep 2013, 02:13
Bunuel wrote:
2. If x is an integer and 9<x^2<99, then what is the value of maximum possible value of x minus minimum possible value of x?
A. 5
B. 6
C. 7
D. 18
E. 20

Also tricky. Notice that x can take positive, as well as negative values to satisfy 9<x^2<99, hence x can be: -9, -8, -7, -6, -4, 4, 5, 6, 7, 8, or 9. We asked to find the value of x_{max}-x_{min}, ans since x_{max}=9 and x_{min}=-9 then x_{max}-x_{min}=9-(-9)=18.
[/square_root]
Answer: D.




Hi bunel
can you explain how we get max,min possible values from -9 to 9
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Re: 12 Easy Pieces (or not?) [#permalink] New post 17 Sep 2013, 02:53
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sivapavan wrote:
Bunuel wrote:
2. If x is an integer and 9<x^2<99, then what is the value of maximum possible value of x minus minimum possible value of x?
A. 5
B. 6
C. 7
D. 18
E. 20

Also tricky. Notice that x can take positive, as well as negative values to satisfy 9<x^2<99, hence x can be: -9, -8, -7, -6, -4, 4, 5, 6, 7, 8, or 9. We asked to find the value of x_{max}-x_{min}, ans since x_{max}=9 and x_{min}=-9 then x_{max}-x_{min}=9-(-9)=18.
[/square_root]
Answer: D.




Hi bunel
can you explain how we get max,min possible values from -9 to 9


Sure.

Since x is an integer and 9<x^2<99, then the least value of x is -9 --> (-9)^2<99 (x cannot be -10 because 10^2=100>99).
The same way, the max value of x is 9 --> 9^2<99 (x cannot be 10 because 10^2=100>99).

Does this make sense?
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Re: 12 Easy Pieces (or not?) [#permalink] New post 18 Sep 2013, 03:42
I have a question about the socks.
How did you know that you are not required to answer for the option that only two socks are the same?
From your answer I gather you took it as "at least" but it was not in the question stem.
What are the rules of these assumptions?
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Re: 12 Easy Pieces (or not?) [#permalink] New post 18 Sep 2013, 12:08
Bunuel wrote:
4. If -3<x<5 and -7<y<9, which of the following represent the range of all possible values of y-x?
A. -4<y-x<4
B. -2<y-x<4
C. -12<y-x<4
D. -12<y-x<12
E. 4<y-x<12

To get max value of y-x take max value of y and min value of x: 9-(-3)=12;
To get min value of y-x take min value of y and max value of x: -7-(5)=-12;

Hence, the range of all possible values of y-x is -12<y-x<12.

Answer: D.




This answer is not 100% right, because there is not the sign <= but only <.
therefore (assuming that X and Y are integers the answer is: (-6-(-4))<Y-X<(8-(-2))
Re: 12 Easy Pieces (or not?)   [#permalink] 18 Sep 2013, 12:08
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