Raju can finish a piece of work in 20 days. He worked at it for 5 days and then Jakob alone finished the remaining work in 15 days. In how many days can both finish it together?

Answer: Option A

Let total work = 60 unit
Work by Raju in one day = $$\frac{60}{20}$$ = 3 unit
5 days → 5 × 3 = 15 unit
Remaining work = 60 - 15 = 45 unit
15 days → 45 unit
1 day → 3 unit (Jakob)
Work done by Raja and Jakob in one day = 3 + 3 = 6
Time = $$\frac{60}{6}$$ = 10 days