A and B can do a work in 15 days and 30 days, respectively. They start working together, but A leaves after 3 days. How much time will B take to complete the remaining work?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 21 days.
Let the total work to be done (LCM of 15 and 30) be 30 units.
Efficiency of A = 30/15 = 2 units/day
Efficiency of B = 30/30 = 1 unit/day
Work done by A and B together in 3 days = (2 + 1) × 3 = 9 units
Remaining work = 30 - 9 = 21 units
Time taken by B to complete remaining work = 21/1 = 21 days