Answer :
Explanation :

Given A,B,C can complete a work in 15,20 and 30 respectively. The total work is given by the LCM of 15, 20, 30 i.e, 60. A's 1 day work = 60/15 = 4 units B's 1 day work = 60/20 = 3 units C's 1 day work = 60/30 = 2 units (A + B + C) worked for 2 days = (4 + 3 + 2) 2 = 18 units  Let B + C worked for x days = (3 + 2) x = 5x units C worked for 2 days = 2 x 2 = 4 units Then, 18 + 5x + 4 = 60 22 + 5x = 60 5x = 38 x = 7.6   Therefore, total number of days taken to complete the work = 2 + 7.6 + 2 = 11.6 = 11 3/5 days.