Question

The petrol rate is increased by $Rs.5$ per litre. Now for $Rs.1320$, $2$ litres less petrol can be bought as compared to the previous rate. Find the increased price of petrol per litre.

Answer 1

Let the original price of one-litre petrol be Rs.$x$

In Rs.$1320$ we obtain $\frac{1320}{x}$ litres of petrol at this rate

If the price is increased by Rs.$5$, then the new price of petrol is Rs. $(x+5)$ per litre.

Then,
In Rs.$1320$ we obtain $\frac{1320}{x+5}$ litres of petrol at the new price

According to the given condition, one gets $2$ litres less petrol on spending Rs.$1320$

Petrol obtained at old price $-$ petrol obtained at new price $=2$

$\therefore$ $\frac{1320}{x}-\frac{1320}{x+5}=2$

$\therefore$ $1320(x+5)-1320x=2x(x+5)$

$\therefore$ $1320x+6600-1320x=2x^2+10x$

$\therefore$ $2x^2+10x-6600=0$

$\therefore$ $x^2+5x-3300=0$

$\therefore$ $x^2+60x-55x-3300=0$

$\therefore$ $(x+60)(x-55)=0$

$\therefore$ $x=-60$ or $x=55$

But $x=-60$ is not possible (price of petrol cannot be negative), so $x=55$

The old price of petrol is Rs.$55$/litre and the increased price is Rs.$60$/litre