x – Total distance in Km.
p – Price per litre in rupees.
Equation of demand function joining two data points (16, 1) and (8, 2) respectively.


– 8y + 8 = x – 16
x – 16 – 8 + 8y = 0
x + 8y – 24 = 0
x = 24 – 8y
y = p
∴ The demand function x = 24 – 8p
Demand ∝ 1/Price