Question

a and b can do a work in 12 and 15 days respectively . if they work on alternate days, a beginning , on what day will the work completed

Answer 1

Alternatively (A+B)'s consecutive two day's work=1/12+1/15=3/20

After 12 days
3/20*6=18/20 

Work remaining 2/20

At 13th day 2/20-1/12=1/60(work remaining)

At 14th day 1/60*15=1/4

It takes 1/4 of 14th day

So total 13 and 1/4days