To do a certain work, the ratio of efficiency of A to that of B is 3 : 7. Working together, they can complete the work in $$10\frac{1}{2}$$ days. They work together for 8 days. 60% of the remaining work will be completed by A alone in

Efficiency ratio of A to B = 3 : 7
Let the efficiency of A and B be 3x and 7x respectively.
Total efficiency = 3x + 7x = 10x
Time taken by A and B to complete the work = $$10\frac{1}{2}$$ = 21/2
Total work = days to complete the work $$\times$$ efficiency = 10x $$\times$$ 21/2 = 105x
Work done in 8 days = 10x $$\times$$ 8 = 80x
Remaining work = 105x - 80x = 25x
60% of the remaining work = 25x $$\times \frac{60}{100} = 15x$$
Time taken by A to complete 15x work = 15x/3x = 5 days
$$\therefore$$ The correct answer is option B.