The owner of a milk store finds that, he can sell 980 litres of milk each week at Rs 14/litre and 1220 litres of milk each week at Rs 16/litre. Assuming linear relation between selling price and demand, how many litres could he sell weekly at Rs 17/litre?

Explanation

Let the selling price and demand be represented on `x`-axis and `y`-axis respectively, then two points `(14,980)` and `(16,1220)` be in the `xy`-plane. Equation of line passing through these points is
`y-980=(1220-980)/(16-14)(x-14)`
`=120(x-14)`
`implies =120x-1680`
`y=120x-700`
Now, at `x=17`
`y=120xx17-700`
`=2040-700`
`=1340`
Therefore, he can sell `1340` litres milk in a weak at `17rs` per litre.