Question:
Two motor mechanics, Raju and Siraj, working together can overhaul a scooter in 6 hours. Raju alone can do the job in 15 hours. In how many hours can Siraj alone do it?
Solution:
Time taken by Raju $=15 \mathrm{~h}$
Work done by Raju in $1 \mathrm{~h}=\frac{1}{15}$
Time taken by Raju and Siraj working together $=6 \mathrm{~h}$
Work done by Raju and Siraj in $1 \mathrm{~h}=\frac{1}{6}$
Work done by Siraj in $1 \mathrm{~h}=($ work done by Raju and Siraj $)-($ work done by Raju $)$
$=\frac{1}{6}-\frac{1}{15}=\frac{5-2}{30}=\frac{3}{30}=\frac{1}{10}$
$\therefore$ Siraj will take $10 \mathrm{~h}$ to overhaul the scooter by himself.