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15 white balls, 25 red balls, 10 blue balls and 20 green

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by arora007 » Fri Jul 30, 2010 8:40 am
In a jar there are 15 white balls, 25 red balls, 10 blue balls and 20 green balls.
How many balls must be taken out in order to make sure we took out 8 of the same color?

a) 8
b) 23
c) 29
d) 32
e) 53


nice one...
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by nithi_mystics » Fri Jul 30, 2010 9:29 am
29 balls

7+7+7+8 = 29
Thanks
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by arora007 » Fri Jul 30, 2010 9:54 am
correct!
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by sumanr84 » Fri Jul 30, 2010 10:28 am
arora007 wrote:In a jar there are 15 white balls, 25 red balls, 10 blue balls and 20 green balls.
How many balls must be taken out in order to make sure we took out 8 of the same color?

a) 8
b) 23
c) 29
d) 32
e) 53


nice one...
From where these questions are popping out ??
I am on a break !!
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by arora007 » Fri Jul 30, 2010 10:32 am
https://www.urch.com/forums/gre-math/867 ... ems-2.html

https://www.scribd.com/doc/25455404/Probability
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by sumanr84 » Fri Jul 30, 2010 11:04 am
arora bhai..I am following your maths thread these days..these Qs are good one as you don't need much math to solve, but rather logical inference, CR kinda..;-)
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by diebeatsthegmat » Thu Aug 26, 2010 10:25 am
nithi_mystics wrote:29 balls

7+7+7+8 = 29
excuse me, can you please explain why there is a number 7 here?
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by Gurpinder » Thu Aug 26, 2010 10:32 am
diebeatsthegmat wrote:
nithi_mystics wrote:29 balls

7+7+7+8 = 29
excuse me, can you please explain why there is a number 7 here?
Read this!

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by GMATGuruNY » Thu Aug 26, 2010 5:25 pm
diebeatsthegmat wrote:
nithi_mystics wrote:29 balls

7+7+7+8 = 29
excuse me, can you please explain why there is a number 7 here?
In order to guarantee that we get 8 of the same color, we need to consider the worst-case scenario. In the problem above, the worst-case scenario would be to choose 7 of each color:

7+7+7+7 = 28.

Thus, choosing only 28 balls isn't sufficient, because we could get only 7 of each color. To guarantee that we get 8 of one of the colors, we need to choose one more ball: 28+1 = 29.

The correct answer is C.

Does this help?
Last edited by GMATGuruNY on Thu Dec 27, 2012 7:30 pm, edited 1 time in total.
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by HPengineer » Thu Aug 26, 2010 6:00 pm
If you picked 28 balls is it not possible that you picked 25 red and 3 green? Therefore not meeting the criteria of pulling out 8 of the same color?
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by GMATGuruNY » Thu Aug 26, 2010 6:08 pm
HPengineer wrote:If you picked 28 balls is it not possible that you picked 25 red and 3 green? Therefore not meeting the criteria of pulling out 8 of the same color?
If you picked 28 balls, you could get 8 of the same color, but getting 8 of the same color wouldn't be guaranteed because you also could choose only 7 of each color. To guarantee that you get 8 of the same color, 1 more ball has to be chosen.
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by sanju09 » Thu Aug 26, 2010 10:37 pm
arora007 wrote:In a jar there are 15 white balls, 25 red balls, 10 blue balls and 20 green balls.
How many balls must be taken out in order to make sure we took out 8 of the same color?

a) 8
b) 23
c) 29
d) 32
e) 53


nice one...
worst case scenario, GMAT's favorite trick

Until 28 balls, as there are 4 different colors, we can at worst expect 7 of each color; just 1 more ball and we definitely have 8 of same color in hand.

[spoiler]C[/spoiler]
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by sahilnyati » Thu Dec 27, 2012 11:09 am
GMATGuruNY wrote:
HPengineer wrote:If you picked 28 balls is it not possible that you picked 25 red and 3 green? Therefore not meeting the criteria of pulling out 8 of the same color?
If you picked 28 balls, you could get 8 of the same color, but getting 8 of the same color wouldn't be guaranteed because you also could choose only 7 of each color. To guarantee that you get 8 of the same color, 1 more ball has to be chosen.
damn correct..!
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by Jeff@TargetTestPrep » Mon Dec 18, 2017 11:42 am
arora007 wrote:In a jar there are 15 white balls, 25 red balls, 10 blue balls and 20 green balls.
How many balls must be taken out in order to make sure we took out 8 of the same color?

a) 8
b) 23
c) 29
d) 32
e) 53
The worst case scenario would be having to draw 7 balls of each color so that we wouldn't have 8 balls of any one color. However, if we were to remove just one more ball, regardless of the color, we would then have 8 balls of one color. Thus, we need to remove 7 x 4 + 1 = 29 balls.

Answer: C

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