The efficiencies of A, B and C are in the ratio 3 : 7 : 5. Working together, they can finish a piece of work in 15 days. A and B work together for 10 days, and C completes the rest of the work. In how many days does C complete the rest of the work?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 25 days
An efficiency ratio can be read as units of work done per day. The total work is then the combined daily work multiplied by the days taken together.
Daily work: A 3 units, B 7 units, C 5 units; together \(3+7+5=15\) units
Total work \(=15\times15=225\) units
A and B in 10 days: \(10\times(3+7)=100\) units
Work left \(=225-100=125\) units
Time for C \(\displaystyle =\frac{125}{5}=25\) days