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# Is a + b > 0 ? 1. 7a - b > 0 2. b - 6a > 0 Thanks.

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Manager
Joined: 13 Oct 2009
Posts: 115
Location: USA
Schools: IU KSB
Followers: 4

Kudos [?]: 55 [1] , given: 66

Is a + b > 0 ? 1. 7a - b > 0 2. b - 6a > 0 Thanks. [#permalink]  30 Oct 2009, 11:59
1
KUDOS
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 100% (00:00) wrong based on 1 sessions
Is a + b > 0 ?

1. 7a - b > 0
2. b - 6a > 0

Thanks.

New Addition: These are PS questions but because I am not able to post a new topic, I am adding these questions to my existing post (DS Forum).

Please help me with the questions below. I am able to solve these but looking for faster way to do so. Can anybody please explain tricks for these questions? Thanks.

1) a couple decides to have 4 children. If they succeed in having 4 children and each child is equally likely to be a boy or a girl, what is the probability that they will have exactly 2 girls and 2 boys?

a. 3/8
b. 1/4
c. 3/16
d. 1/8
e. 1/16

2) A square wooden plaque has a square brass inlay in the center, leaving a wooden strip of uniform width around the brass square. If the ratio of the brass area to the wooden area is 25 to 39, whick of the following could be, in inches, the width of the wooden strip?

I. 1
II 3
III 4

I only
II only
I and II only
I and III only
I, II, and III

3) An ice-cream sundae consists of two ice-cream scoops, one flaver per scoop, and one topping. How many different types of sundaes can be prepared if four ice-cream flavors and two toppings are available?

a. 12
b. 14
c. 16
d. 18
e. 20

Thanks.

Last edited by swatirpr on 17 Nov 2009, 05:25, edited 1 time in total.
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Senior Manager
Joined: 18 Aug 2009
Posts: 304
Followers: 3

Kudos [?]: 123 [1] , given: 9

Re: Is a+b > 0 ? [#permalink]  30 Oct 2009, 18:17
1
KUDOS
C

(A) and (B) by themselves does not gives enough info (use substitution)

Combining them together
6a<b<7a

Case 1 a is positive.
Above equation can be satisfied for b lying between 6a and 7a. So b is also positive.

Case 2 a is negative.
We cannot find b lying between 6a and 7a (a=1 -6<??<-7)

So only Case 1 remains, using which we can say a+b>0. Sufficient
Manager
Joined: 13 Oct 2009
Posts: 115
Location: USA
Schools: IU KSB
Followers: 4

Kudos [?]: 55 [0], given: 66

a couple decides to have 4 children; types of Sundaes? [#permalink]  17 Nov 2009, 05:29
New Addition: These are PS questions but because I am not able to post a new topic, I am adding these questions to my existing post (DS Forum).

Please help me with the questions below. I am able to solve these but looking for faster way to do so. Can anybody please explain tricks for these questions? Thanks.

1) a couple decides to have 4 children. If they succeed in having 4 children and each child is equally likely to be a boy or a girl, what is the probability that they will have exactly 2 girls and 2 boys?

a. 3/8
b. 1/4
c. 3/16
d. 1/8
e. 1/16

2) A square wooden plaque has a square brass inlay in the center, leaving a wooden strip of uniform width around the brass square. If the ratio of the brass area to the wooden area is 25 to 39, whick of the following could be, in inches, the width of the wooden strip?

I. 1
II 3
III 4

I only
II only
I and II only
I and III only
I, II, and III

3) An ice-cream sundae consists of two ice-cream scoops, one flaver per scoop, and one topping. How many different types of sundaes can be prepared if four ice-cream flavors and two toppings are available?

a. 12
b. 14
c. 16
d. 18
e. 20

Thanks.
Senior Manager
Joined: 18 Aug 2009
Posts: 304
Followers: 3

Kudos [?]: 123 [1] , given: 9

Re: a couple decides to have 4 children; types of Sundaes? [#permalink]  17 Nov 2009, 05:56
1
KUDOS
swatirpr wrote:
New Addition: These are PS questions but because I am not able to post a new topic, I am adding these questions to my existing post (DS Forum).

Please help me with the questions below. I am able to solve these but looking for faster way to do so. Can anybody please explain tricks for these questions? Thanks.

1) a couple decides to have 4 children. If they succeed in having 4 children and each child is equally likely to be a boy or a girl, what is the probability that they will have exactly 2 girls and 2 boys?

a. 3/8
b. 1/4
c. 3/16
d. 1/8
e. 1/16

2) A square wooden plaque has a square brass inlay in the center, leaving a wooden strip of uniform width around the brass square. If the ratio of the brass area to the wooden area is 25 to 39, whick of the following could be, in inches, the width of the wooden strip?

I. 1
II 3
III 4

I only
II only
I and II only
I and III only
I, II, and III

3) An ice-cream sundae consists of two ice-cream scoops, one flaver per scoop, and one topping. How many different types of sundaes can be prepared if four ice-cream flavors and two toppings are available?

a. 12
b. 14
c. 16
d. 18
e. 20

Thanks.

(1) I got 3/8
Listed the favorable ways BBGG, BGBG, BGGB (x2=6) and total ways 2x2x2x2=16
probablity = 3/8

don't know why 2nd is stuck... skipping to goto 3rd
getting 20 there
case 1: same 2 flavor with different topping... possibilities 4x2=8
case 2: different 2 flavors (4x3)/2=6 [divide by 2 'coz it is the same combination with the flavors reversed]
...with different topping 6x2=12
Total 8+12=20
Senior Manager
Joined: 18 Aug 2009
Posts: 304
Followers: 3

Kudos [?]: 123 [1] , given: 9

Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes? [#permalink]  17 Nov 2009, 06:15
1
KUDOS
and 2nd is E it seems
ratio-problem-64346.html
Manager
Joined: 13 Oct 2009
Posts: 115
Location: USA
Schools: IU KSB
Followers: 4

Kudos [?]: 55 [0], given: 66

Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes? [#permalink]  17 Nov 2009, 08:38

Quote:
(1) I got 3/8
Listed the favorable ways BBGG, BGBG, BGGB (x2=6) and total ways 2x2x2x2=16 Can you please explain how you calculated total ways here.
probability = 3/8

You got all the answers right.

Thanks again.

[Reveal] Spoiler:
1. A
2. E
3. E
Manager
Joined: 29 Oct 2009
Posts: 211
GMAT 1: 750 Q50 V42
Followers: 78

Kudos [?]: 802 [0], given: 18

Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes? [#permalink]  17 Nov 2009, 09:42
1) Probability of boy = Probability of girl = 1/2

Therefore, Probability of 2 boys and 2 girls = (1/2)*(1/2)*(1/2)*(1/2)*[4!/(2!*2!)]

That is number of ways of selecting 4 objects in which two are similar.

= 3/8

3) (4C2)*(2C1) + (4C1)*(2C1) = 12 + 8 = 20
_________________

Click below to check out some great tips and tricks to help you deal with problems on Remainders!
compilation-of-tips-and-tricks-to-deal-with-remainders-86714.html#p651942

1) Translating the English to Math : word-problems-made-easy-87346.html

Senior Manager
Joined: 18 Aug 2009
Posts: 304
Followers: 3

Kudos [?]: 123 [0], given: 9

Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes? [#permalink]  17 Nov 2009, 17:42
swatirpr wrote:

Quote:
(1) I got 3/8
Listed the favorable ways BBGG, BGBG, BGGB (x2=6) and total ways 2x2x2x2=16 Can you please explain how you calculated total ways here.
probability = 3/8

You got all the answers right.

Thanks again.

[Reveal] Spoiler:
1. A
2. E
3. E

Total ways- for first kid, it can be either B or G so two possibilities, similarly for 2nd, 3rd and 4th... 2x2x2x2
Manager
Joined: 13 Oct 2009
Posts: 115
Location: USA
Schools: IU KSB
Followers: 4

Kudos [?]: 55 [0], given: 66

Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes? [#permalink]  17 Nov 2009, 19:34
Quote:
(1) I got 3/8
Listed the favorable ways BBGG, BGBG, BGGB (x2=6) and total ways 2x2x2x2=16 Can you please explain how you calculated total ways here.
probability = 3/8

Total ways- for first kid, it can be either B or G so two possibilities, similarly for 2nd, 3rd and 4th... 2x2x2x2

Got it, thanks again.
Re: Is a+b > 0 ?; a couple decides to have 4 children; Sundaes?   [#permalink] 17 Nov 2009, 19:34
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