Question

Ravi can do a piece of work in 15 hours while Raman can do it in 12 hours how long will go take to do it working together

Answer 1

ravi can do work in=15h
raman can do work in=12h
they both will do work
$\frac{1}{15} + \frac{1}{12} \\ \frac{4 + 5}{60} \\ = \frac{9}{60} \\ = \frac{60}{9} = \frac{20}{3}h$