A and B can complete a task in 40 days and 16 days respectively. A started the task alone and then after 12 days B joined him till the completion of the task. How long did the task last after B joined the task?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 8 days
Let the total work be the LCM of 40 and 16 i.e 80 unit
Efficiency = Total work/Total time
Efficiency of A = 80/40 = 2
Efficiency of B = 80/16 = 5
A/c to question A started the task alone and then after 12 days B joined him till the completion of the task.
Let A and B together work for x days
(2 × 12) + {(2 + 5) × x} = 80
24 + 7x = 80
7x = 56 , x = 8