Question

a can do a piece of work in 15 hours while B can do it in 12 hours how long will both take to do it working together

Answer 1

A's 1 hour work = 1/15
B's 1 hour work = 1/12
(A+B)'s 1 hour work = 1/15+1/12
= (4+5)/60
= 9/60
Time taken by A and B to complete the job working together
= 60/9 hours
= 20/3 hours
Ans. = 6 hours 40 minutes