We can also solve this with AP.
Notice the series
15:00-20
15:03-23
15:06-26
.
.
.
15:42-x
common difference is 3, 1st term is 20, no. of terms is 15
so last term=1st term+(no. of term-1)common difference
x=20+14*3=62
We need to find the population at 15:44, the next addition will be 15:45. So, strategically 15:42 population is fine till here.
Now it has been given that at eac interval of 10 minutes 8 students are leaving, starting from 15:10,
so, at 15:10=-8
15:20=-8
15:30=-8
15:40=-8
total student left=-32
the next batch of 8 student will leave at 15:50.
As we have got the 62 as population when 3 are added every 3 minute, now we got 32 as 8 leaving every 10 min from the given time 15:03 and 15:10 respectively.
Therefore at 15:44 there will 62-32=30 students left.
Bunuel
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