A and B can complete work alone in 20 days and 60 days respectively. They began the work together but A left the work after some days and B completed the remaining work in 12 days. After how many days from the beginning A left the work?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 12 days
the work done by B in 12 days
The work rate of B = 1/60 of the work per day
In 12 days, the work done by B = 1/60 × 12 = 12/60 = 1/5
Since B completed 1/5 of the work,
the remaining work to be completed by A and B together before A left = 1 − 15 = 45
Combined work rate of A and B = 1/20 + 1/60 = 1/15 of the work per day
Days A and B worked together = 4/5 ÷ 1/15 = 4/5 × 15 = 12 days