Rahul can complete a work in 12 days and Ayush in 15 days. If they work together for 3 days, then the fraction of work that will be left is:

Let us assume total work to be L.C.M(12,15) be 60 unit (you can assume any number but for the sake of calculation it is advised to take L.C.M of the given numbers)   Efficiency of Rahul = 60/12 = 5 unit/day Efficiency of Ayush = 60/15 = 4 unit/day Total efficiency of Rahul and Ayush = 5 + 4 = 9 unit/day According to the question, They work together for 3 days Total work done = 9 x 3 = 27 unit Remaining work = (60-27) = 33 unit Fraction of remaining work = 33/60 =11/20