## Elementary Technical Mathematics

$\frac{5}{6}$ h
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