A certain number of men can finish a piece of work in 30 days. If however............How many men were there originally?

Question

A certain number of men can finish a piece of work in 30 days.
If however there were 15 men less it will take 30 days more for the work to be finished.
How many men were there originally?

Answer 1

Speed reduced to half by 15 people implies 15 people make half of the work group, making the total strength = 30

N men can do 1 work in 30 days
(N - 15) men can do 1 work in 60 days
Speed of N men = 1 work / 30 days
Speed of (N - 15) = 1 work / 60 days
Speed of 1 man = 1 work / (30×N days) = 1 work / (60×(N - 15) days)
30N = 60N - 900
30N = 900
N = 30 men.