A can do a piece of work in 18 days and the efficiency of B and C is 15 unit/day and 13 unit/day respectively. Work done by A and C together in 1 day is 3 units more than B and C together. Then find the time taken by B is how much percent more than time taken by A ?

20 %

                             B            C

          Efficiency      15         13

ATQ,

(A+C) - (B+C) = 3

  A - B = 3     (A's eff. is 3 unit more than B's)

Efficiency of A = 15 + 3 = 18

Hence,

                                           A               B

        efficiency                     18             15

Time taken by A & B             15             18

 Total work = Efficiency × Number of days

So ratio of efficiency and time is inverse to each other 

Now, more time is taken by B i.e 3R

    Required %  = \(\frac{3R}{15R}\) × 100 = 20%