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Math Expert V
Joined: 02 Sep 2009
Posts: 56302
A machine is made up of two components, A and B. Each component either  [#permalink]

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Difficulty:   25% (medium)

Question Stats: 73% (01:13) correct 27% (01:13) wrong based on 64 sessions

### HideShow timer Statistics A machine is made up of two components, A and B. Each component either works or fails. The failure or non-failure of one component is independent of the failure or non-failure of the other component. The machine works if at least one of the components works.

If the probability that each component works is $$\frac{2}{3}$$, what is the probability that the machine works?

A. $$\frac{1}{9}$$

B. $$\frac{4}{9}$$

C. $$\frac{1}{2}$$

D. $$\frac{2}{3}$$

E. $$\frac{8}{9}$$

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Re: A machine is made up of two components, A and B. Each component either  [#permalink]

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1
Bunuel wrote:
A machine is made up of two components, A and B. Each component either works or fails. The failure or non-failure of one component is independent of the failure or non-failure of the other component. The machine works if at least one of the components works.

If the probability that each component works is $$\frac{2}{3}$$, what is the probability that the machine works?

A. $$\frac{1}{9}$$

B. $$\frac{4}{9}$$

C. $$\frac{1}{2}$$

D. $$\frac{2}{3}$$

E. $$\frac{8}{9}$$

Method 1:

Machine works if atleast one component works i.e. we get the following cases for machine to work

Case 1: First Component works and Second Fails = Probability = (2/3)*(1/3) = 2/9

Case 2: First Component Fails and Second Works = Probability = (1/3)*(2/3) = 2/9

Case 3: First Component works and Second Works = Probability = (2/3)*(2/3) = 4/9

Total Probability = (2/9)+(2/9)+(4/9) = 8/9

Method 2:

Probability of machine to work = 1 - Probability of machine to fail to wrk

i.e. Probability of machine to work = 1 - Probability of Both components failing = 1- (1/3)*(1/3) = 1- (1/9) = 8/9

Hope this helps!!!
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##### General Discussion
Director  G
Joined: 20 Feb 2015
Posts: 790
Concentration: Strategy, General Management
Re: A machine is made up of two components, A and B. Each component either  [#permalink]

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Bunuel wrote:
A machine is made up of two components, A and B. Each component either works or fails. The failure or non-failure of one component is independent of the failure or non-failure of the other component. The machine works if at least one of the components works.

If the probability that each component works is $$\frac{2}{3}$$, what is the probability that the machine works?

A. $$\frac{1}{9}$$

B. $$\frac{4}{9}$$

C. $$\frac{1}{2}$$

D. $$\frac{2}{3}$$

E. $$\frac{8}{9}$$

A works but B doesn't = 2/3*1/3=2/9
B works but A doesn't = 2/9
both A and B work = 2/3*2/3=4/9
p(machine works) = sum of above = 2/9 + 2/9 + 4/9 = 8/9
CrackVerbal Representative B
Joined: 14 Aug 2014
Posts: 18
Location: India
GMAT 1: 660 Q50 V29 GMAT 2: 680 Q51 V30 GMAT 3: 720 Q51 V35 Re: A machine is made up of two components, A and B. Each component either  [#permalink]

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The only case in which machine will not work : Both A and B fail

Probability that machine will work = 1 - Probability of both A and B failing

Probability of A failing = 1 - 2/3 = 1/3

Probability of B failing = 1 - 2/3 = 1/3

Probability of both A and B failing = (1/3)*(1/3) = 1/9

Probability that machine will work = 1 - 1/9 = 8/9
Non-Human User Joined: 09 Sep 2013
Posts: 11704
Re: A machine is made up of two components, A and B. Each  [#permalink]

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_________________ Re: A machine is made up of two components, A and B. Each   [#permalink] 17 Jul 2019, 00:11
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