Work done = time × efficiency Calculation: Total work =LCM of (X,Y and Z ) Total work = LCM of (50,100 and 36) = 900 units Now, Efficiency of X =900∕50=18 units Efficiency of Y=900∕100=9 units Efficiency of Z=900∕36=25 units Now, Time taken by X=50 days Time taken by Y=100 days Time taken by Z=36 days Time taken by (X+Z)=900∕(18+25)=20.93 days When ( X and Z ) work together, they will complete the work first.