A car can travel $12\dfrac{1}{2}$km in 1 litre of petrol. How much distance can it travel in $42\dfrac{3}{5}$ litres of petrol?

Given:

Distance travelled in 1 litre of petrol = $12\dfrac{1}{2}$ km

= $\dfrac{25}{2}$ km $\hspace{1cm}$ [Converting mixed to improper fraction]

Distance travelled in $42\dfrac{3}{5}$ litres of petrol = ?

Number of litres = $42\dfrac{3}{5}$ = $\dfrac{213}{5}$ litres

Distance travelled in $\dfrac{213}{5}$ litres of petrol = (Distance travelled in 1 litre) x (Number of litres)

Substituting the values in above, we get:

$\begin{array}{ll} = \Big(\dfrac{25}{2} \times \dfrac{213}{5}\Big)\text{ km} \\ = \Big(\dfrac{5}{2} \times \dfrac{213}{1}\Big)\text{ km} & \text{[Simplifying 25 and 5 ⇒ Divide by 5 ]} \\ = \Big(\dfrac{5 \times 213}{2 \times 1}\Big) \text{ km} \\ = \dfrac{1065}{2}\text{ km} \\ = 532 \dfrac{1}{2}\text{ km} & \text{[Converting improper fraction to mixed fraction]} \end{array}$

∴ The distance travelled in $42\dfrac{3}{5}$ litres of petrol = $532\dfrac{1}{2}$ km.