Question

Ram can complete an work in 10 hours ajith in 12 hours and suresh in 15 hrs

Answer 1

all can do in = 1/10+ 1/12 + 1/15
=(6+5+4)/60
= 15/60
= 1/4
so all can do in 4 days

Answer 2

total work =60

ram do 6 work in 1 hour

Ajit 5 in one hour

Suresh 4 in 1 hour

so left work after 2 hour and after ram leave is 60-30=30

anjit left work 3hour before completion so Ajit and Suresh did 18 work in next 2 hours

so remaining work 12 is done by Suresh 12/4 = in 3 hours

so total time is 2+2+3=7 hours

hope it helps...regards