Question

A, B and C alone can complete a work in *
20 days, 30 days and 60 days, respectively. A
works alone, however on every third day, he
takes the help of B and C. In how many days
will the work be completed?​

Answer 1

2 day's work = (1 /20 x 2 ) = 1 /10

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

work done in 3 days = (1/10+1/10)=1/5

NOW 1/5 work is done in 3 days

Whole work will be done in (3 x 5) = 15 days