AFCAT Model Paper 7

Given:
A is 2 times efficient as B
B can finish work alone in 36 days
Both started working together
A left the work 3 days before the completion of work
Calculation:
Since efficiency is always inversely proportional to time. Time taken by B = 2 units = 36 days
Time taken by A = 1 unit = 18 days
Let Total work = Lcm of 18 and 36 = 36 units
⇒ Efficiency of B = 1 unit/day
⇒ Efficiency of A = 2 units/day
Since A left the work 3 days before the completion of the work
So in the last 3 days, B will work alone
⇒ Work done by B in 3 days = 1 × 3 = 3 units
⇒ Remaining work = 36 - 3 = 33 units
Here the remaining work was done by A and B together
Time taken by both A and B to complete the reamining work =

33

3

=11 days
∴ Total time taken to complete the work = 11 + 3 = 14 days.