A does 60% of the work in 18 days. He then calls in B, and they together finish the remaining work in 4 days. How long would B alone take to do the whole work?
Show answer & explanation
Correct answer: D
Explanation
Given:
A completes 60% of the work = 18 days
Remaining work = 40%
A and B together complete the remaining work = 4 days
A's rate = 60% / 18 = 1/30 (work/day)
Remaining work = 40% = 2/5
A + B's rate = (2/5) / 4 = 1/10 (work/day)
B's rate = (A + B) − A = 1/10 − 1/30 = 1/15
B's time to complete the work alone = 1 ÷ (1/15) = 15 days