A job can done by 3 skilled men in 15 days or by 5 boys in 30 days. How many days will they take if they work together?

Question: A job can done by 3 skilled men in 15 days or by 5 boys in 30 days. How many days will they take if they work together?

Solution:
3 men's 1 day work = 1/15 part
and 5 boys 1 day's work = 1/30 part

∴ (3 men's + 5 boy's) 1 day work = (1/15 + 1/30) = (2 +1)/30 = 3/30 = 1/10 part

∴ 3 men and 5 boys will complete the work in 10 days.