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A metal company's old machine makes bolts at a constant rate of 100

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A metal company's old machine makes bolts at a constant rate of 100 [#permalink]

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New post 14 Sep 2017, 04:03
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A metal company's old machine makes bolts at a constant rate of 100 bolts per hour.The company's new machine makes bolts at a constant rate of 150 bolts per hour. If both machines start at the same time and continue making bolts simultaneously, how many minutes will it take the two machines to make a total of 300 bolts?

A. 36
B. 72
C. 120
D. 144
E. 180
[Reveal] Spoiler: OA

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Kudos [?]: 128687 [0], given: 12182

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Re: A metal company's old machine makes bolts at a constant rate of 100 [#permalink]

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New post 14 Sep 2017, 04:28
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Bunuel wrote:
A metal company's old machine makes bolts at a constant rate of 100 bolts per hour.The company's new machine makes bolts at a constant rate of 150 bolts per hour. If both machines start at the same time and continue making bolts simultaneously, how many minutes will it take the two machines to make a total of 300 bolts?

A. 36
B. 72
C. 120
D. 144
E. 180


First way: In an hour you will make: 100+150 = 250.

So in two -> 500 > 300.
Which means C,D,E falls immediately.
Also, everything under an hour, A falls.

-> and the answer is B. 72.

Second way:

12 minutes = 1/5 of an hour, so that's 150/5 + 100/5 = 30+20 = 50.
300 would need 6 times that.
So 12*5 = 72 minutes.

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Re: A metal company's old machine makes bolts at a constant rate of 100 [#permalink]

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New post 14 Sep 2017, 05:07
Bunuel wrote:
A metal company's old machine makes bolts at a constant rate of 100 bolts per hour.The company's new machine makes bolts at a constant rate of 150 bolts per hour. If both machines start at the same time and continue making bolts simultaneously, how many minutes will it take the two machines to make a total of 300 bolts?

A. 36
B. 72
C. 120
D. 144
E. 180

Total bolts in 1 hour of both machines: 250
So 300 bolts/250 bolts=6/5
60/5*6= 72 minutes

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Re: A metal company's old machine makes bolts at a constant rate of 100 [#permalink]

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New post 17 Sep 2017, 14:10
In one hour, they'll do 250 bolts. There are still 50 missing, and since they make 250 per hour, they'll need 50/250 * 60 (minutes) = 12 minutes to do the remaining 50 bolts.

Hence, B.

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Re: A metal company's old machine makes bolts at a constant rate of 100 [#permalink]

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New post 18 Sep 2017, 05:45
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Expert's post
Bunuel wrote:
A metal company's old machine makes bolts at a constant rate of 100 bolts per hour.The company's new machine makes bolts at a constant rate of 150 bolts per hour. If both machines start at the same time and continue making bolts simultaneously, how many minutes will it take the two machines to make a total of 300 bolts?

A. 36
B. 72
C. 120
D. 144
E. 180


We can let t = the time in hours the machines work together; thus:

100t + 150t = 300

250t = 300

t = 30/25 = 6/5 hours, which is 6/5 x 60 = 72 minutes.

Answer: B
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Kudos [?]: 828 [1], given: 5

Re: A metal company's old machine makes bolts at a constant rate of 100   [#permalink] 18 Sep 2017, 05:45
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