Question

John drove $48$ miles and used $2$ gallons of gasoline. How many gallons of gasoline will he use if he drives $78$ miles?

Answer 1

Step-1: Direct proportion concept:

The direct proportion is the connection between two values whose ratio is a constant.

As the quantity of gasoline is increased, it will increase the miles driven by John.

$\Rightarrow$The gasoline used is directly proportional to the distance covered by John.

John used $2$ gallons to drive $48$ miles.

Consider $y$ gallons is used to drive $78$ miles.

Step-2: Find the gallons of gasoline used:

The gasoline used is directly proportional to the distance covered.

$\Rightarrow \frac{\mathrm{Gallons}\mathrm{of}\mathrm{gasoline}\mathrm{used}}{\mathrm{Miles}\mathrm{covered}}=\mathrm{constant}$

$\Rightarrow \frac{2}{48}=\mathrm{constant}$

$\Rightarrow \frac{\mathrm{y}}{78}=\mathrm{constant}$

Equating the above two equations,

$$\begin{gathered} \Rightarrow \frac{\mathrm{y}}{78}=\frac{2}{48} \\ \Rightarrow \mathrm{y}=\frac{2}{48}\times 78 \\ \Rightarrow \mathrm{y}=3.25 \end{gathered}$$

Hence, John used $\mathbf{3}\mathbf{.}\mathbf{25}$ gallons of gasoline to drive $\mathbf{78}$ miles.