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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 am; Location: India; Thanked: 51 times; Followed by:27 members; GMAT Score:670

Probability - breaking the jar ?

by arora007 » Fri Jul 30, 2010 8:57 am

The probability of pulling a black ball out of a glass jar is 1/X. The probability of pulling a black ball out of a glass jar and breaking the jar is 1/Y. What is the probability of breaking the jar?

a) 1/(XY).
b) X/Y.
c) Y/X.
d) 1/(X+Y).
e) 1/(X-Y).

Good one...

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Source: Beat The GMAT — Problem Solving | Fri Jul 30, 2010 8:57 am

nithi_mystics: Senior | Next Rank: 100 Posts; Posts: 55; Joined: Mon Sep 07, 2009 9:11 pm; Location: California; Thanked: 4 times

by nithi_mystics » Fri Jul 30, 2010 9:40 am

b) X/Y

probability of pulling a black ball out of a glass jar and breaking the jar = probability of pulling a black ball out of a glass jar * probability of breaking the jar

1/y = 1/x * probability of breaking the jar

==> probability of breaking the jar = x/y

Thanks
Nithi

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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 am; Thanked: 32 times; Followed by:3 members

by Gurpinder » Fri Jul 30, 2010 9:46 am

arora007 wrote:The probability of pulling a black ball out of a glass jar is 1/X. The probability of pulling a black ball out of a glass jar and breaking the jar is 1/Y. What is the probability of breaking the jar?

a) 1/(XY).
b) X/Y.
c) Y/X.
d) 1/(X+Y).
e) 1/(X-Y).

Good one...

to get the probability of something AND something happening you multiply the two probabilities

so that means that 1/x * ______ = 1/y so just divide 1/x / 1/y which equals to x/y

so the answer is B

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 am; Location: India; Thanked: 51 times; Followed by:27 members; GMAT Score:670

by arora007 » Fri Jul 30, 2010 9:56 am

both of u deserve a 51. God bless!!

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babuxavier: Senior | Next Rank: 100 Posts; Posts: 84; Joined: Tue Oct 02, 2012 9:02 am; Followed by:1 members

by babuxavier » Wed Nov 21, 2012 9:43 am

IMO B

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Bill@VeritasPrep: GMAT Instructor; Posts: 1248; Joined: Thu Mar 29, 2012 2:57 pm; Location: Everywhere; Thanked: 503 times; Followed by:192 members; GMAT Score:780

by Bill@VeritasPrep » Wed Nov 21, 2012 9:45 am

nithi_mystics wrote:b) X/Y

probability of pulling a black ball out of a glass jar and breaking the jar = probability of pulling a black ball out of a glass jar * probability of breaking the jar

1/y = 1/x * probability of breaking the jar

==> probability of breaking the jar = x/y

Yup. The keyword here is AND: black ball AND jar breaks. Nicely done.

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 am; Location: New York, NY; Thanked: 39 times; Followed by:22 members

by Jeff@TargetTestPrep » Mon Dec 18, 2017 5:53 pm

arora007 wrote:The probability of pulling a black ball out of a glass jar is 1/X. The probability of pulling a black ball out of a glass jar and breaking the jar is 1/Y. What is the probability of breaking the jar?

a) 1/(XY).
b) X/Y.
c) Y/X.
d) 1/(X+Y).
e) 1/(X-Y).

We can let the probability of breaking the jar = p; thus:

(1/X)p = (1/Y)

p = (1/Y)/(1/X)

p = X/Y

Answer: B

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