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# A new Machine is bought by a factory to produce 2 parts, A

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Senior Manager
Joined: 25 Dec 2003
Posts: 360
Location: India
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Kudos [?]: 17 [0], given: 0

A new Machine is bought by a factory to produce 2 parts, A [#permalink]  06 Jun 2004, 21:26
A new Machine is bought by a factory to produce 2 parts, A and B. A and B when assembled produce C. During the testing stages of the machine, 1 out of 10 in A is defective and 2 out of 10 in B are defective. What is the probability of C being defective.

a. 0.02
b. 0.20
c. 0.28
d. 0.32
e. 0.72
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Joined: 31 Dec 1969
Location: India
Concentration: General Management, Strategy
GMAT 1: 710 Q49 V0
GMAT 2: 740 Q40 V50
GMAT 3: 700 Q48 V38
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Kudos [?]: 89 [0], given: 87136

P(non-defective)=(9/10)*(8/10)=72/100=0.72
P(defective)=1-0.72=0.28
C.
Manager
Joined: 02 Jun 2004
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Intern
Joined: 21 May 2004
Posts: 2
Location: Atlanta
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Kudos [?]: 0 [0], given: 0

another approach.. [#permalink]  09 Jun 2004, 08:40
P(C) defective = P(A) defective + P(B) defective - P (A and B) defective

= .2 + .1 - .2 * .1 = .3 - .02 = .28
Senior Manager
Joined: 25 Dec 2003
Posts: 360
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Kudos [?]: 17 [0], given: 0

The correct answer is indeed 0.28.

Thanks for all the explaination.
Regards
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Intern
Joined: 23 Jun 2004
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Another great one where no calculation is required. We know that the upper limit is 30% ( if all defective A's and B's are seperated)and lower limit is 20% (if all defective A's and B's are joined together). Only one answer left

Should I be thinking like this or should I be looking to calculate
Senior Manager
Joined: 25 Dec 2003
Posts: 360
Location: India
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Kudos [?]: 17 [0], given: 0

HI Maneesh

In my opinion, it is best to calculate in any probability question. I used to strulle in Combinatins and Prob questions. But thru this forum, things looks much easier. All it needs is to put the words in to figures. Mental calculations or close approximation does not help in here.

Example. You may have answers whic are very close 1/3 or2/5 ..it is difficult. Practice using calculation. The more you do, the better you get. I bet on this.

Regards
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Manager
Joined: 07 May 2004
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Hi guys, actually we have solved this question before...

Of course, C is the answer.
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