We know that if the distance increases quantity of petrol also increases, such that the ratio of distances and the ratio of the required quantity of petrol will remain the same. That means here distance and required quantity of petrol are in proportion.
Given quantity of petrol required to cover 135 km = 3l
Let the quantity of petrol required to cover 495 km = xl
Then 135 : 495 = 3 : x
If the ratios are equal, the product of means = The product of the extremes
⇒ 135 × x = 495 × 3
⇒ x = 11
∴ The quantity of petrol required to cover 495 km = 11
