Answer
$\frac{5}{6}$ h
Work Step by Step
Let the mechanic spent $\frac{1}{3}$ h changing the spark plug, $\frac{1}{4}$ h changing the air filter, $\frac{1}{4}$ h changing the oil and oil filter.
Therefore total time spent on servicing the car = $\frac{1}{3}$ h + $\frac{1}{4}$ h + $\frac{1}{4}$ h
= $ \frac{1}{3} \times$ $\frac{4}{4}$ + $ \frac{1}{4} \times$ $\frac{3}{3}$ + $ \frac{1}{4} \times$ $\frac{3}{3}$
= $\frac{4}{12}$ + $\frac{3}{12}$ + $\frac{3}{12}$
= $\frac{10}{12}$ h
=$\frac{5}{6}$ h
