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If Robert can assemble a model car in 30 minutes and Craig

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If Robert can assemble a model car in 30 minutes and Craig  [#permalink]

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New post 15 May 2017, 07:15
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A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

100% (00:43) correct 0% (00:00) wrong based on 22 sessions

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If Robert can assemble a model car in 30 minutes and Craig can assemble the same model car in 20 minutes, how long would it take them, working together, to assemble the model car?

(A) 12 minutes
(B) 13 minutes
(C) 14 minutes
(D) 15 minutes
(E) 16 minutes

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Re: If Robert can assemble a model car in 30 minutes and Craig  [#permalink]

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New post 15 May 2017, 07:44
Top Contributor
rohan2345 wrote:
If Robert can assemble a model car in 30 minutes and Craig can assemble the same model car in 20 minutes, how long would it take them, working together, to assemble the model car?

(A) 12 minutes
(B) 13 minutes
(C) 14 minutes
(D) 15 minutes
(E) 16 minutes


A quick approach is to assign a NICE VALUE to the job of assembling the model car.
Let's choose a value that works well with 30 minutes and 20 minutes.
How about 60.
So, let's say that the entire job consists of assembling 60 pieces.

Robert can assemble a model car in 30 minutes
Rate = output/time
= 60/30
= 2 pieces per minute

Craig can assemble the same model car in 20 minutes
Rate = output/time
= 60/20
= 3 pieces per minute

How long would it take them, working together, to assemble the model car?
Their COMBINED RATE = 2 + 3 = 5 pieces per minute
time = output/rate
= 60/5
= 12 minutes

Answer:

Cheers,
Brent
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Re: If Robert can assemble a model car in 30 minutes and Craig &nbs [#permalink] 15 May 2017, 07:44
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