Bilal can do a work in 15 days and Jalal in 12 days. If they work on it together for 4 days, the fraction of work that is left is________?

A. 3/5
B. 4/7
C. 2/5
D. 1/4
Part of work completed by Bilal in a day = 1/15 Part of work completed by Jalal in a day = 1/12 Part of work completed by them in a day = (1/15)+(1/12) = 3/20 Part of work completed by them in 4 days = (3/20)*4 = 3/5 Fraction of work left
= 1-(3/5)
= 2/5