Given: The company initially planned to use m computer systems for 17 days. After the first day, 4 systems crashed each day, and the work took 8 extra days, so the total time became 25 days.
Find: The value of m.
Without any crash, total work required is
17m
computer-days.
With crashes, the work done day-wise forms an arithmetic progression:
m+(m−4)+(m−8)+⋯+(m−4×24)
because there are 25 days in total.
Equating actual work to required work:
17m=m+(m−4)+(m−4×2)+⋯+(m−4×24)
so
17m=25m−4(1+2+⋯+24)Now,
1+2+⋯+24=224×25=300Substituting,
17m=25m−4×300
25m−17m=1200
8m=1200
m=150Therefore, the value of m is 150. The correct option is B.