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Math Expert V
Joined: 02 Sep 2009
Posts: 56236

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Difficulty:   45% (medium)

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

### HideShow timer Statistics 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

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Math Expert V
Joined: 02 Sep 2009
Posts: 56236

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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 $$14*3 - 8*4 = 10$$.

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Manager  G
Joined: 01 Sep 2016
Posts: 190
GMAT 1: 690 Q49 V35 ### Show Tags

I think this is a high-quality question and I agree with explanation. in love with this question. AMAZING
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Intern  B
Joined: 24 Oct 2016
Posts: 29

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This is a high quality question.

Posted from my mobile device
Intern  B
Joined: 04 Oct 2016
Posts: 17

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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 $$14*3 - 8*4 = 10$$.

Can someone please explain this in detail. How did we get 42 and 40 in numerators.
Math Expert V
Joined: 02 Sep 2009
Posts: 56236

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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 $$14*3 - 8*4 = 10$$.

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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Intern  B
Joined: 04 Oct 2016
Posts: 17

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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 $$14*3 - 8*4 = 10$$.

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

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