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A basket contains 5 apples, of which 1 is spoiled and the [#permalink]
02 Mar 2009, 11:37

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25% (medium)

Question Stats:

74% (01:41) correct
26% (00:52) wrong based on 216 sessions

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple?

Re: PS: Probability Apples [#permalink]
02 Mar 2009, 13:22

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bmiller0731 wrote:

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple?

a) 1/5 b) 3/10 c) 2/5 d) 1/2 e) 3/5

p (both apples are not spoiled) = 4C2/5C2 = 4*3/5*4 = 3/5

p (one of the apple spoiled) = 1-3/5 = 2/5 _________________

Your attitude determines your altitude Smiling wins more friends than frowning

Re: PS: Probability Apples [#permalink]
02 Mar 2009, 13:46

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Total Apples = 5 Spoiled Apples = 1 Not Spoiled Apples = 4

Possible outcomes: (Apple 1) Not Spoiled, (Apple 2) Spoiled; = (4/5)*(1/4) = 4/20 or 2/10. OR (Apple 1) Spoiled, (Apple 2) Not Spoiled; = (1/5)*(4/4) = 4/20 or 2/10.

Re: PS: Probability Apples [#permalink]
07 Mar 2009, 09:41

bmiller0731 wrote:

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple?

Re: PS: Probability Apples [#permalink]
07 Mar 2009, 09:58

bmiller0731 wrote:

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple?

a) 1/5 b) 3/10 c) 2/5 d) 1/2 e) 3/5

prob (one spoiled and one good) = (no. of ways of selecting 1 spoiled and 1 good)/(total no. of ways of selecting 2 apples)

prob = (select one good AND one bad)/(select any two out of 5) = 4c1*1C1 / 5c2 = 2/5

Re: A basket contains 5 apples, of which 1 is spoiled and the [#permalink]
25 Mar 2012, 11:12

7

This post received KUDOS

Expert's post

mymbadreamz wrote:

I didn't understand. Could someone explain?

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple? A. 1/5 B. 3/10 C. 2/5 D. 1/2 E. 3/5

Direct combinatorial approach: Probability=\frac{# \ of \ favorable \ outcomes}{total \ # \ of \ outcomes}: Favorable outcomes: C^1_1*C^1_4 --> C^1_1 choosing one rotten out of 1 and C^1_4 choosing any for the second apple; Total # of outcomes: C^2_5, choosing 2 apples out of 5; P=\frac{C^1_1*C^1_4}{C^2_5}=\frac{2}{5}.

Reverse combinatorial approach: Let's count the probability of the opposite event and subtract this value from 1. The opposit event will be if out of 2 apples both are good, so P=1-\frac{C^2_4}{C^2_5}=\frac{2}{5}.

Direct probability approach: P=\frac{1}{5}*\frac{4}{4}+\frac{4}{5}*\frac{1}{4}=\frac{2}{5}: probability of {first apple rotten, second apple good} plus the probability of {first apple good, second apple rotten}.

Reverse probability approach: Again 1- the probability of the opposite event --> P=1-\frac{4}{5}*\frac{3}{4}=\frac{2}{5}.

Re: A basket contains 5 apples, of which 1 is spoiled and the [#permalink]
27 Aug 2012, 10:52

+1 C

Total number of combinations: 5!/3! = 20 Number of combinations that include the spoiled apple: When the spoiled apple is the first apple picked: 1*4= 4 When the spoiled apple is the second apple picked: 4*1 = 4 Total: 8

Probability: 8/20 = 2/5

C. _________________

"Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can."

Re: A basket contains 5 apples, of which 1 is spoiled and the [#permalink]
27 Aug 2012, 13:09

bmiller0731 wrote:

A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the possibility that the 2 apples selected will include the spoiled apple?

A. 1/5 B. 3/10 C. 2/5 D. 1/2 E. 3/5

Computing directly probabilities and using the complementary event:

P(spoiled apple selected) = 1 - P(no spoiled apple selected) = 1 - P(first apple not spoiled)*P(second apple also not spoiled) = 1 - (4/5)*(3/4) = 1 - 3/5 = 2/5.

Answer C _________________

PhD in Applied Mathematics Love GMAT Quant questions and running.

Re: A basket contains 5 apples, of which 1 is spoiled and the [#permalink]
25 Sep 2012, 08:37

1

This post received KUDOS

No. of apples that are not spoiled = 4 No. of apples that are spoiled = 1

The question is asking us to find out the probability of finding one spoiled apple among the 2 randomly selection ...

We can have 2 scenarios , Scenario A) where the first apple selected is not spoiled , and the second apple selected is spoiled and Scenario B) where the first apple selected is spoiled and the second selected is not spoiled ..

Scenario A) We have four apples out of five that are not spoiled , therefore probability is 4/5 , the second apple is a spoiled one out of the remaining 4 , therefore we have overall probability of this outcome as (4/5) x (1/4) = 4/20

Scenario B ) We have only one apple out of 5 that is spoiled so probability is 1/5 , the second apple can be one from any 4 remaining thefore 4/4... Probability of this outcome is (1/5) x (4/4) = 1/5 ....

We must add these two scenarios therefore we get 4/20 + 1/5 = 8/20 = 2/5 (C) _________________

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