A, B, and C can do a job in 12, 15, and 20 days, respectively. All three work together for 4 days. Then A leaves; B and C continue, but at only 3/4 of their normal daily hours. How many more days are needed to finish?
Show answer & explanation
Correct answer: B
Explanation
Given:
A = 12 days
B = 15 days
C = 20 days
All three worked for 4 days.
Subsequently, B and C work at only 3/4 of their capacity.
According to the formula:
Work done in 1 day = 1/12 + 1/15 + 1/20
1/12 + 1/15 + 1/20
= 5/60 + 4/60 + 3/60
= 12/60
= 1/5
Work done in 4 days = 4 × 1/5 = 4/5
Remaining work = 1 − 4/5 = 1/5
Combined 1-day capacity of B + C
= 1/15 + 1/20
= 4/60 + 3/60
= 7/60
At 3/4 capacity
= 7/60 × 3/4
= 21/240
= 7/80
Time required = (1/5) ÷ (7/80)
= 1/5 × 80/7
= 16/7
= days