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M19-28

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M19-28  [#permalink]

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New post 16 Sep 2014, 01:06
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E

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  45% (medium)

Question Stats:

72% (01:31) correct 28% (01:56) wrong based on 204 sessions

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Re M19-28  [#permalink]

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New post 16 Sep 2014, 01:06
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Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E
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Re M19-28  [#permalink]

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New post 12 Aug 2017, 02:41
I think this is a high-quality question and I agree with explanation. in love with this question. AMAZING
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Re: M19-28  [#permalink]

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New post 08 Oct 2017, 23:20
This is a high quality question.

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Re: M19-28  [#permalink]

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New post 03 Sep 2018, 09:57
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.
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Re: M19-28  [#permalink]

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New post 03 Sep 2018, 23:47
mischiefmanaged wrote:
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.


First 3 students entered the lab at 15:03. Next:
15:06;
15:12;
...
15:39
Last 3 students entered the lab at 15:42.

As you can see we have multiples of 3 from 3 to 42 inclusive. How many multiples of 3 are there in this range? (42 - 3)/3 + 1 = 14.

First 8 student group left the lat at 15:10.
15:20
15:30
15:40.
4 groups, 8 students each, left the lab.
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Re: M19-28  [#permalink]

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New post 04 Sep 2018, 01:27
Bunuel wrote:
mischiefmanaged wrote:
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.


First 3 students entered the lab at 15:03. Next:
15:06;
15:12;
...
15:39
Last 3 students entered the lab at 15:42.

As you can see we have multiples of 3 from 3 to 42 inclusive. How many multiples of 3 are there in this range? (42 - 3)/3 + 1 = 14.

First 8 student group left the lat at 15:10.
15:20
15:30
15:40.
4 groups, 8 students each, left the lab.


Thank you very much.
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Re: M19-28   [#permalink] 04 Sep 2018, 01:27
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