A group of men decided to do a job in 6 days, but 18 men dropped out every day. If the job was completed in 8 days, then how many men initially decided to do the job.
Answer & explanation
Correct answer: option 2
Let initial number of men be M
Total work = no. of men x days = 6M
Thus, the equation formed on this condition:
M + (M - 18) + (M - 36) .......... = 6M
Using the formula of sum in Arithmetic Progression,
Sn = n/2[2a + (n − 1) × d]
Here, a = M, d = -18
$\frac{8}{2}$[2M + 7(-18)] = 6M
8M - 126 x 4 = 6M
2M = 504 or M = 252