A and B together can complete a piece of work in 15 days. A is 150% more efficient worker than B.

A and B together can complete a piece of work in 15 days. A is 150% more efficient worker than B. How long will A take to complete the work alone? (a) 20 days (b) 21 days (c) 21.4 days (d) 22.5 days

Correct option (c) 21.4 days Explanation:  A : B efficiency (100+150) : 100% 250 : 100(A+B) Efficiency 5 : 2=7 units/days Total work= 15 days ×7 units = 105  A can complete the whole work in = 105/5 = 21 days