A man dug a ditch in 3 hours and his daughter can dig the sa

A man dug a ditch in 3 hours and his daughter can dig the same size ditch in 5 hours. Working together, how long will it take them to dig the ditch?

In 1 hr the man dig 1/3 portion of the ditch ,,In 1 hr his daughter can dig 1/5 portion of the ditch hence in 1 hr they together can ditch 1/3 +1/5 =8/15 portion of the ditch hence they together can dig the ditch in 1/ 8/15=15/8hrs ANS