A can do a piece of work in 20 days and B can do it in 30 days. How long will they take to do the work together?
Work done by A in 1 day =120, Work done by B in 1 day =130
Work done by A and B in 1 day =120+130
=3+260=560=112 of the work
Total number of days required to finish the work by A and B
=1112=12days