A and B together can do a piece of work in 40 days, while B and C together can do the same work in 30 days. If A alone can do the same work in 60 days. If efficiency of C increased by 100/3%, then in how many days C alone can do 7/8 th of the same work.

Correct option is A

Total work = 120 unit (LCM of 40, 30 and 60)
Efficiency of A and B together = 120/40=3 unit/day
Efficiency of B and C together = 120/30=4 unit/day
Efficiency of A = 120/60=2 unit/day
So, efficiency of B = 3 – 2 = 1 unit/day
And, efficiency of C = 4 – 1 = 3 unit/day
Increased efficiency of C = 3 +3×1/3=4 unit/day
Required days