Nayan can do a piece of work in 36 days. Rishi can do the same piece of work in 48 days and Nishu can do the same in 42 days. Nayan and Nishu worked for 6 days handed it over to Rishi. Rishi worked for some days and handed it over again to Nayan and Nishu 10 days before completing the work. Then, Nishu and Nayan completed the work. For how many days did Rishi worked with them?

a) 8 and 8/21 days

b) 6 and 7/23 days

c) 6 and 11/21 days

d) 6 and 11/23 days

Ans. A

Nayan and Nishu worked for beginning 6 days => work done = 6/36 + 6/42 = 1/6 + 1/7 = 13/42

Nayan and Nishu worked for ending 10 days => work done = 10/36 + 10/42

Total Work done by rishi = 1 – 13/42 – 10/36 – 10/42 = 44 / (6 x 6 x 7) = a

Work done by rishi in 1 day = 1/48 = b

No of days Rishi worked = a / b = 8 and 8/21 days.

Hence option a) is correct.