A and B can finish a piece of work in 15 days and 20 days, respectively. If A and B work on alternate days, how many days will it take to complete the work (A starts the work)?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 17.
Total work = LCM(15, 20) = 60 units
Efficiency of A = 60 ÷ 15 = 4 units/day
Efficiency of B = 60 ÷ 20 = 3 units/day
Work done in 2 days (A + B) = 4 + 3 = 7 units
16 days work = 56 units
Remaining work done by A = (60 - 56)/4 = 4/4 = 1 day
total days = 16 + 1 = 17 days