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
= B’s1 hour work
= C’s 1 hour work
= 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,
++=1 ⇒9(x–3)+8(x–4)+6x=72 ⇒ 9x – 27 + 8x – 32 + 6x = 72
⇒ 23x = 131
∴ x==5.7 hours.