B is 20% more efficient than A. If B was 60% more efficient than A, then, B could complete the work in 18 days lesser than days taken by A. What fraction of work would be left after 12 days, if A and B work together?

Solution

Ratio of efficiency A : B = 5 : 6 Time taken by A and B will be 6t and 5t respectively. Now, if B is 60% more efficient than A, the ratio of efficiency will become Ratio of B => 5 × 160/100 = 8 Ratio of time taken = 8t : 5t So, 6t/x = 8/5 x = 15t/4 Now, according to question 6t – 15t/4 = 18 => 9t/4 = 18 => t = 8 Therefore, time taken by A and B to complete the work will be 48 days and 40 days respectively In 12 days, total amount of work done will be, 12/48 + 12/40 = 22/40 Fraction of left work = 1 – 22/40 = 18/40 = 9/20