AFCAT Model Paper 7

Given:
A, B and C can do a piece of work in 24, 20 and 40 days respectively
C left the work 4 days before the completion of the work
Calculation:
Speed of A = work to do / time it takes to do the work =

1

24

Speed of B = work to do / time it takes to do work =

1

20

Speed of C =

1

40

.
When they work together they take t days to complete the work with the given condition. So according to equation:
⇒ Work done by A=

t

24

⇒ Work done by B=

t

20

⇒ Work done by C=

t−4

40

So, According to the question

t

24

+

t

20

+

t−4

40

=1
∴ Time taken t = 9.43 days.