Number of hours Ravi required do a piece of work : 15 hours
Number of hours Raman required do a piece of work : 12 hours
Work done by Ravi in one hour: \(\frac{1}{15}\)
Work done by Raman in one hour: \(\frac{1}{12}\)
Work done by Ravi and Raman together in one hour: \(\frac{1}{15}+\frac{1}{12}=\frac{9}{60}=\frac{3}{20}\)
∴ They can do the work together in \(\frac{20}{3}\) hours = \(6\frac{2}{3}\) = 6 hours 40 min