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At 15:00, 20 students were in the computer lab. Starting at 15:03, and

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Bunuel
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At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink] New post   13 Jun 2019, 23:56
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69% (02:25) correct 31% (02:26) wrong based on 177 sessions
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At 15:00, 20 students were in the computer lab. Starting at 15:03, and every three minutes thereafter, 3 students entered the lab. Meanwhile, beginning at 15:10 and every ten minutes thereafter, 8 students exited 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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E
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Re: At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink] New post   14 Jun 2019, 00:24
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Bunuel wrote:
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


From 15:03 till 15:44, number of multiples of 3 are 14 = 3*14 = 42 students entered the lab
So, Total students entered lab = 42

From 15:10 till 15:44, number of 10 multiples are 4 = 4*8 = 32 students left the lab

So, Net students present in lab at 15:44 = 20 + 42 - 32 = 30

IMO Option E
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Re: At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink] New post   14 Jun 2019, 00:46
Bunuel wrote:
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


Number of multiples of 3 in 44 minutes = 44/3=14 so 42 additions
Number of multiples of 10 in 44 min = 4 so 32 deletions
So Net 10 addition to 20 IMO E 30
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Re: At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink] New post   14 Jun 2019, 02:14
Bunuel wrote:
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


from 1500 to 1544 total students entered ; 14*3 ; 42 and left ; 32
net ; 42-32 ; 10
inital class was of 20 @ 1500 so total students; 10+20 ; 30 @ 15:44
IMO E
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Re: At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink] New post   01 Oct 2023, 01:42
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Bunuel wrote:
At 15:00, 20 students were in the computer lab. Starting at 15:03, and every three minutes thereafter, 3 students entered the lab. Meanwhile, beginning at 15:10 and every ten minutes thereafter, 8 students exited the lab. How many students were in the computer lab at 15:44?

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


Students began entering the lab every 3 minutes starting at 15:03 and continued until 15:42. This gives a total of \(\frac{42-3}{3} + 1 = 14\) intervals where 3 students each entered. On the other hand, students started leaving the lab every 10 minutes beginning at 15:10 and the last group left at 15:40, resulting in \(\frac{40-10}{10} + 1 = 4\) intervals where groups of 8 students each departed. Therefore, the net increase in students in the lab is \(14*3 - 4*8 = 6\).


Answer: E
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Re: At 15:00, 20 students were in the computer lab. Starting at 15:03, and [#permalink]
01 Oct 2023, 01:42
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