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# The probability of pulling a black ball out of a glass jar

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Senior Manager
Joined: 13 Jun 2005
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Location: Haverhill, MA
The probability of pulling a black ball out of a glass jar [#permalink]

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26 Jan 2006, 18:17
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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).

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SVP
Joined: 16 Oct 2003
Posts: 1798

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26 Jan 2006, 20:01
A = black
B = break
C = black and break

p(A) AND p(B) = p(C)
1/X * p(B) = 1/Y
p(B) = X/Y

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VP
Joined: 20 Sep 2005
Posts: 1016

Kudos [?]: 39 [0], given: 0

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26 Jan 2006, 20:20
Give it a shot..B

Prob. of pulling a black ball and breaking = prob. of pulling out a black ball * prob of breaking the jar.

Prob. of pulling a black ball and breaking = 1/y = x/y*1/x = 1/x*x/y.

Hence, the prob. of breaking = x/y.

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GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5032

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Location: Singapore

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26 Jan 2006, 20:24
P(pull a black ball) = 1/X
P(pull a black ball and break jar) = P(pull a black ball) * P(break the jar) = 1/Y

I assume both are independent events.

So P(break the jar) = 1/Y / 1/X = X/Y

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CEO
Joined: 20 Nov 2005
Posts: 2892

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Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

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27 Jan 2006, 02:01
P(A+B) = P(A) * P(B)

1/Y = 1/X * P(B)

P(B) = X/Y
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Kudos [?]: 337 [0], given: 0

27 Jan 2006, 02:01
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