A and B can together complete a task in 18 hours. After 6 hrs A leaves. B takes 36 hrs to finish rest of the task. How many hours would A have taken to do the task if he worked alone ?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 ie 27.
Let the total number of units of work = 108
A and B can do in 18 hrs = 108/18 = 6 units
Each hour they both can do 6 units.
For 6 hours, they both worked and so 36 units are done.
108 - 36 = 72 units of work done by B alone in 36 hours.
72/36 = 2 units/day
Therefore,
a + b = 6
a = 6 - 2
a = 4 units/day
If A worked alone, then = 108/4 = 27 hours