Question

A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

A. 12 days
B. 15 days
C. 16 days
D. 18 days

Answer 1

Work done in 3 days=(3/20)+(1/30)+(1/60)=1/5
Remaining work=4/5
If 1/5 work is done in 3 days then,
4/5 work is done in (3*5*4)/5=12days
Total no. of days will become 12+3=15days for the complete work to be done.:)

Answer 2

Given
A can do a piece of work in 20 daysA;s one day work = 1/20
A's 2 days work = 2/20 = 1/10

B can do a piece of work in 30 daysB's one day work = 1/30

A can do a piece of work in 60 daysA's one day work = 1/60


(A+B+C)'s one day work = 1/20 + 1/30 + 1/60
                                       =6/60
                                       1/10

Again,
Work done in three days = 1/10 + 1/10
                                      =1/5

So,
1/5 work will done in 3 days
Hence
whole work will done  in = 5*3
                                      = 15 days