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

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BSchool Forum Moderator
Joined: 29 Jan 2015
Posts: 1423
Location: India
WE: General Management (Non-Profit and Government)
If Robert can assemble a model car in 30 minutes and Craig  [#permalink]

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Updated on: 10 Jul 2019, 04:56
1
00:00

Difficulty:

5% (low)

Question Stats:

85% (00:53) correct 15% (01:23) wrong based on 61 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

Source: Nova GMAT
Difficulty Level: 500

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Originally posted by rohan2345 on 15 May 2017, 07:15.
Last edited by SajjadAhmad on 10 Jul 2019, 04:56, edited 1 time in total.
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Joined: 12 Sep 2015
Posts: 4015
Re: If Robert can assemble a model car in 30 minutes and Craig  [#permalink]

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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.
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

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

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02 Apr 2019, 19:20
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

The combined rate of Robert and Craig is 1/20 + 1/30 = 3/60 + 2/60 = 5/60. We can interpret this rate as “They can assemble 5 model cars in 60 minutes.” Since time is the reciprocal of rate, it would take them 60/5 = 12 minutes to complete one car.

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Re: If Robert can assemble a model car in 30 minutes and Craig   [#permalink] 02 Apr 2019, 19:20
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