A man, a woman and a boy can complete a job in 3, 5 and 15 days, respectively. How many boys must assist 1 man and 1 woman to complete the job in $\frac{1}{5}$ of a day?

If A, B and C can do a work in 6 days, 9 days and 11 days, respectively, then, working together, how many days will they take to do the work?

Sara can finish a work in 18 days and Tara can complete the same work in 15 days. Tara worked for 10 days and left the job. In how many days can Sara finish the remaining work alone?

40 men can complete a work in 30 days. However, if 10 men leave the group, how many days will the group take to complete the work?