A can complete a certain piece of work in 40 days. B is 25% more efficient than A and C is 28% more efficient than B. They work together for 5 days. The remaining work will be completed by B alone, in:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e 
days
Explanation:
Let the efficiency of A be x.
Efficiency of B = 25% more efficient than A = 1.25x
Efficiency of C = 28% more efficient than B = 1.25x × 128/100 = 1.6x
Efficiency ratio of A, B and C = x: 1.25x : 1.6x = 20 : 25 :32
Total work = efficiency × time = 20 × 40 = 800 units
5 days work = (20 + 25 + 32) × 5 = 77 × 5 = 385 units
Remaining work = 800 - 385 = 415 units
Time taken to complete work by B = 415/25 =