Question

a can do a piece of work in 10 days and b in 15 days how long they will take longer to complete it

Answer 1

A can do in = 10days
in day, work done by A = 1/10

B can do in = 15days
in day, work done by A = 1/15

total work by them in 1day = 1/10 + 1/15 = (3+2)/30 = 1/6
to complete work, time needed = 1/(1/6) = 6 days
they can complete it in 6days.