Last visit was: 24 Apr 2024, 11:24 It is currently 24 Apr 2024, 11:24

Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
SORT BY:
Date
avatar
Intern
Intern
Joined: 15 Mar 2014
Posts: 7
Own Kudos [?]: [0]
Given Kudos: 2
Send PM
RC & DI Moderator
Joined: 02 Aug 2009
Status:Math and DI Expert
Posts: 11169
Own Kudos [?]: 31889 [1]
Given Kudos: 290
Send PM
Manager
Manager
Joined: 03 Jul 2016
Status:Countdown Begins...
Posts: 242
Own Kudos [?]: 144 [0]
Given Kudos: 80
Location: India
Concentration: Technology, Strategy
Schools: IIMB
GMAT 1: 580 Q48 V22
GPA: 3.7
WE:Information Technology (Consulting)
Send PM
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [0]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Expert Reply
RMD007 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.


Hi Bunuel, I tried to refer other posts for this answer but I did not understand. Can you please elaborate this? how M=7k+3..


The row begins with blue marble and ends with red marble. What cases can we have?

{blue, white, red} = 7*0 + 3
{blue, white, red, green, black, yellow, pink} {blue, white, red} = 7*1 + 3
{blue, white, red, green, black, yellow, pink} {blue, white, red, green, black, yellow, pink} {blue, white, red} = 7*2 + 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} = 7*3 + 3
...

As you can see in any case the number of marbles must be a multiple of 7 plus 3.

Hope it's clear.
Intern
Intern
Joined: 25 Jan 2013
Posts: 30
Own Kudos [?]: 14 [0]
Given Kudos: 5909
Location: United States
Concentration: General Management, Entrepreneurship
Schools: Johnson '21
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Bunuel wrote:
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

To get the least value of \(x^2*y\), which obviously will be negative, try to maximize absolute value of \(x^2*y\), as more is the absolute value of a negative number "more" negative it is (the smallest it is).

To maximize \(|x^2*y|\) pick largest absolute values possible for \(x\) and \(y\): \((-\frac{1}{3})^2*(-\frac{1}{2})=-\frac{1}{18}\). Notice that: -1/18<-1/36<-1/50<-1/100, so -1/100 is the largest number and -1/18 is the smallest number (we cannot obtain -1/6 from x^2*y or else it would be the correct answer).

Answer: D.


Is it not the other way around where -1/100 is the least number and -1/18 is the max negative number. I would have picked A as the answer.
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [0]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Expert Reply
vs224 wrote:
Bunuel wrote:
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

To get the least value of \(x^2*y\), which obviously will be negative, try to maximize absolute value of \(x^2*y\), as more is the absolute value of a negative number "more" negative it is (the smallest it is).

To maximize \(|x^2*y|\) pick largest absolute values possible for \(x\) and \(y\): \((-\frac{1}{3})^2*(-\frac{1}{2})=-\frac{1}{18}\). Notice that: -1/18<-1/36<-1/50<-1/100, so -1/100 is the largest number and -1/18 is the smallest number (we cannot obtain -1/6 from x^2*y or else it would be the correct answer).

Answer: D.


Is it not the other way around where -1/100 is the least number and -1/18 is the max negative number. I would have picked A as the answer.


No.

-1/18 = ~-0.06 and -1/100 = -0.01

-0.06 < -0.01



As you can see -1/100 is to the right of -1/18.

Attachment:
MSP3701ihg50f15748di7300006532e8b04fda4c6c.gif
MSP3701ihg50f15748di7300006532e8b04fda4c6c.gif [ 1.41 KiB | Viewed 3649 times ]
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [0]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Expert Reply
Shef08 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.




Why is it not A? Can’t we simply subtract x from y? Then the answer will be A?

Posted from my mobile device



You can only apply subtraction when the signs of inequalities are in the opposite directions:

If \(a>b\) and \(c<d\) (signs in opposite direction: \(>\) and \(<\)) --> \(a-c>b-d\) (take the sign of the inequality you subtract from).
Example: \(3<4\) and \(5>1\) --> \(3-5<4-1\).

You can only add inequalities when their signs are in the same direction:

If \(a>b\) and \(c>d\) (signs in same direction: \(>\) and \(>\)) --> \(a+c>b+d\).
Example: \(3<4\) and \(2<5\) --> \(3+2<4+5\).

For more check Manipulating Inequalities.
Intern
Intern
Joined: 22 Dec 2018
Posts: 11
Own Kudos [?]: 8 [0]
Given Kudos: 201
Concentration: Healthcare, International Business
WE:Medicine and Health (Health Care)
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Bunuel wrote:
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

Also no need for algebraic manipulation. 1/10^(n+1) is 10 times less than 1/10^n, and both when expressed as decimals are of a type 0.001 (some number of zeros before 1) --> so the given expression to hold true we should have: 0.001<0.00737<0.01, which means that n=2 (1/10^n=0.01 --> n=2).

Answer: B.


Hi Bunuel,

I am unable to understand how did we get 0.001 for 1/10^(n+1).
From what i understand 1/10^(n+1) is of form 1/10^n x 10^1.
Would you please explain?

Thanks
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [1]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
1
Kudos
Expert Reply
swatjazz wrote:
Bunuel wrote:
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

Also no need for algebraic manipulation. 1/10^(n+1) is 10 times less than 1/10^n, and both when expressed as decimals are of a type 0.001 (some number of zeros before 1) --> so the given expression to hold true we should have: 0.001<0.00737<0.01, which means that n=2 (1/10^n=0.01 --> n=2).

Answer: B.


Hi Bunuel,

I am unable to understand how did we get 0.001 for 1/10^(n+1).
From what i understand 1/10^(n+1) is of form 1/10^n x 10^1.
Would you please explain?

Thanks


1/10^1 = 0.1
1/10^2 = 0.01
1/10^3 = 0.001
...

Thus, both 1/10^(n+1) and 1/10^n when expressed as decimals are of a type 0.001 (some number of zeros before 1). So, not that both are equal to 0.001 but both will be 0. followed by some number of zeros before 1.
Manager
Manager
Joined: 12 Aug 2020
Posts: 53
Own Kudos [?]: 6 [0]
Given Kudos: 572
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
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.



How do you pick a smart number? Can you show how you strategize about this, since we need to make sure its divisible by18 but also the subsequent calculations wont result in fractional values that dont make sense.
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [0]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Expert Reply
testtakerstrategy wrote:
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.



How do you pick a smart number? Can you show how you strategize about this, since we need to make sure its divisible by18 but also the subsequent calculations wont result in fractional values that dont make sense.



We need a number 2/9 of which is an integer, so the number should be a multiple of 9. We also want (x*2/9)*3/4 = x*1/6 to be in integer, so the number also should be a multiple of 2 (and 3 but since we already established that the number should be a multiple of 9, then we can ignore that here). So, the number should be a multiple of 9*2 = 18.


Number plugging:


How to Do Math on the GMAT Without Actually Doing Math
The Power of Estimation for GMAT Quant
How to Plug in Numbers on GMAT Math Questions
Number Sense for the GMAT
Can You Use a Calculator on the GMAT?
Why Approximate?
GMAT Math Strategies — Estimation, Rounding and other Shortcuts
The 4 Math Strategies Everyone Must Master, Part 1 (1. Test Cases and 2. Choose Smart Numbers.)
The 4 Math Strategies Everyone Must Master, part 2 (3. Work Backwards and 4. Estimate)
Intelligent Guessing on GMAT
How to Avoid Tedious Calculations on the Quantitative Section of the GMAT
GMAT Tip of the Week: No Calculator? No Problem.
The Importance of Sorting Answer Choices on the GMAT

For more check Ultimate GMAT Quantitative Megathread

Hope it helps.
User avatar
Intern
Intern
Joined: 23 Nov 2022
Posts: 3
Own Kudos [?]: 0 [0]
Given Kudos: 2
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Are these really sub-600 questions...? If so, these must be the areas I am weakest in...
Math Expert
Joined: 02 Sep 2009
Posts: 92902
Own Kudos [?]: 618787 [0]
Given Kudos: 81588
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Expert Reply
username10101 wrote:
Are these really sub-600 questions...? If so, these must be the areas I am weakest in...


No, those are quite tricky 700+ questions. The name "12 Easy Pieces (or not?)" is meant to be ironic, juxtaposing the simplicity suggested by 'easy pieces' with the underlying complexity of the questions.
User avatar
Intern
Intern
Joined: 23 Nov 2022
Posts: 3
Own Kudos [?]: 0 [0]
Given Kudos: 2
Send PM
12 Easy Pieces (or not?) [#permalink]
Bunuel wrote:
username10101 wrote:
Are these really sub-600 questions...? If so, these must be the areas I am weakest in...


No, those are quite tricky 700+ questions. The name "12 Easy Pieces (or not?)" is meant to be ironic, juxtaposing the simplicity suggested by 'easy pieces' with the underlying complexity of the questions.


*Breathing a sigh of relief*

Lol. Thank you, Bunuel.

Doing Charles' study plan, on week 1, and got mixed up (and humbled) with the tags.
Senior Manager
Senior Manager
Joined: 29 Oct 2015
Posts: 474
Own Kudos [?]: 259 [0]
Given Kudos: 302
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
Bunuel , KarishmaB, Can you please suggest an easier way to figure out that n = 2 in this case ; Can I infer that n = 2 because there are two zero es in front of 737 ; hence n= 2 will satisfy the inequality ?  Hence , .001 < .00737 < .01 ; How do you arrive at this conclusion all on a sudden that n = 2 ? Please help.
Bunuel wrote:
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

There is no need for algebraic manipulation to answer this question.

\(\frac{1}{10^{n+1} }\) is 10 times smaller than \(\frac{1}{10^n}\). When expressed as decimals, both have the form 0.001 (with a varying number of zeros preceding the 1). For the given expression to be valid, we should have: \(0.001 < 0.00737 < 0.01\). This implies that \(n=2\) (since \(\frac{1}{10^n}=0.01\), then \(n=2\)).

Answer: B.

­
Tutor
Joined: 16 Oct 2010
Posts: 14817
Own Kudos [?]: 64898 [1]
Given Kudos: 426
Location: Pune, India
Send PM
12 Easy Pieces (or not?) [#permalink]
1
Kudos
Expert Reply
sayan640 wrote:
Bunuel , KarishmaB, Can you please suggest an easier way to figure out that n = 2 in this case ; Can I infer that n = 2 because there are two zero es in front of 737 ; hence n= 2 will satisfy the inequality ?  Hence , .001 < .00737 < .01 ; How do you arrive at this conclusion all on a sudden that n = 2 ? Please help.
Bunuel wrote:
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

There is no need for algebraic manipulation to answer this question.

\(\frac{1}{10^{n+1} }\) is 10 times smaller than \(\frac{1}{10^n}\). When expressed as decimals, both have the form 0.001 (with a varying number of zeros preceding the 1). For the given expression to be valid, we should have: \(0.001 < 0.00737 < 0.01\). This implies that \(n=2\) (since \(\frac{1}{10^n}=0.01\), then \(n=2\)).

Answer: B.

­

­
Use the Estimation concept. 

\(0.00737 = \frac{737}{10^5}\)

737 is less than 1000 but greater than 100. 

\(\frac{100}{10^5}<\frac{737}{10^5} < \frac{1000}{10^5}\)

\(\frac{1}{10^3}<\frac{737}{10^5} < \frac{1}{10^2}\)

So n = 2

Answer (B)

Check this video on Estimations: 
https://youtu.be/4Wy7BrQrjkM
 ­

Originally posted by KarishmaB on 15 Apr 2024, 21:06.
Last edited by KarishmaB on 16 Apr 2024, 00:35, edited 1 time in total.
Senior Manager
Senior Manager
Joined: 29 Oct 2015
Posts: 474
Own Kudos [?]: 259 [0]
Given Kudos: 302
Send PM
12 Easy Pieces (or not?) [#permalink]
Thank you  KarishmaB for the wonderful explanation :)
KarishmaB wrote:
sayan640 wrote:
Bunuel , KarishmaB, Can you please suggest an easier way to figure out that n = 2 in this case ; Can I infer that n = 2 because there are two zero es in front of 737 ; hence n= 2 will satisfy the inequality ?  Hence , .001 < .00737 < .01 ; How do you arrive at this conclusion all on a sudden that n = 2 ? Please help.
Bunuel wrote:
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

There is no need for algebraic manipulation to answer this question.

\(\frac{1}{10^{n+1} }\) is 10 times smaller than \(\frac{1}{10^n}\). When expressed as decimals, both have the form 0.001 (with a varying number of zeros preceding the 1). For the given expression to be valid, we should have: \(0.001 < 0.00737 < 0.01\). This implies that \(n=2\) (since \(\frac{1}{10^n}=0.01\), then \(n=2\)).

Answer: B.

­

­
Use the Estimation concept. 

\(0.00737 = \frac{737}{10^5}\)

737 is less than 1000 but greater than 100. 

\(\frac{100}{10^5}<\frac{737}{10^5} < \frac{1000}{10^5}\)

\(\frac{1}{10^3}<\frac{737}{10^5} < \frac{1}{10^2}\)

So n = 2

Answer (B)

Check this video on Estimations: https://youtu.be/4Wy7BrQrjkM
 ­

­
Senior Manager
Senior Manager
Joined: 21 Nov 2021
Posts: 437
Own Kudos [?]: 209 [0]
Given Kudos: 344
Send PM
Re: 12 Easy Pieces (or not?) [#permalink]
sayan640 wrote:
Bunuel , KarishmaB, Can you please suggest an easier way to figure out that n = 2 in this case ; Can I infer that n = 2 because there are two zero es in front of 737 ; hence n= 2 will satisfy the inequality ?  Hence , .001 < .00737 < .01 ; How do you arrive at this conclusion all on a sudden that n = 2 ? Please help.
Bunuel wrote:
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

There is no need for algebraic manipulation to answer this question.

\(\frac{1}{10^{n+1} }\) is 10 times smaller than \(\frac{1}{10^n}\). When expressed as decimals, both have the form 0.001 (with a varying number of zeros preceding the 1). For the given expression to be valid, we should have: \(0.001 < 0.00737 < 0.01\). This implies that \(n=2\) (since \(\frac{1}{10^n}=0.01\), then \(n=2\)).

Answer: B.

­


If it were me, I'd get rid of the pesky decimal.

.00737*10^5 =737

So multiply all three by 10^5:

10^(4-n)<737<10^(5-n)

737 is less than 1000 and greater than 100, meaning n must be 2 by observation.

Posted from my mobile device
GMAT Club Bot
Re: 12 Easy Pieces (or not?) [#permalink]
   1   2   3 
Moderators:
Math Expert
92902 posts
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne