AFCAT Model Paper 10

Given:
A can finish a work in 8 hours
B can finish a work in 9 hours
C can finish a work in 12 hours
A left the work 3 hours before the completion of the work
B left the work 4 hours before the completion of the work
Concept Used:
1 hour work = 1/n, where n = number of hours to complete the work
Calculation :
According to the concept used
A’s 1 hour work =

1

8

B’s1 hour work =

1

9

C’s 1 hour work =

1

12

Let the work is completed in ‘x’ hours.
A worked for (x – 3) hours.
B worked for (x – 4) hours.
C worked for x hours.
Thus, we have,

(x–3)

8

+

(x–4)

9

+

x

12

=1
⇒9(x–3)+8(x–4)+6x=72
⇒ 9x – 27 + 8x – 32 + 6x = 72
⇒ 23x = 131
∴ x=

131

23

=5.7 hours.