A piece of work was to be completed in 40 days, a number of men employed upon it did only half the work in 24 days, 16 more men were then set on and the work was completed in the specified time, how many men were employed at first?

Let N men were employed at first
∵ N men do 1/2 of the work in 24 days
∴ 1 man do the whole work in 24 x 2 x N = 48N days
Now, from the question,
(N + 16) men do the remaining work (1 - 1/2) = 1/2 in (40 - 24) = 16 days
∴ 1 man do the whole work in 16 x 2 x (N + 16) days
∴ 48N = 32(N + 16)
∴ N = 32 men