A alone can do a piece of work in 10 days and B alone can do it in 15 days. In how many days will A and B together do the same work?
Number of days A required do a piece of work : 10 days
Number of days B required do a piece of work : 15 days
Work done by A in one day: 
Work done by B in one day: 
Work done by A and B together in one day: 
= 
= 
They can do the work together in 6 days
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