Question

A car owner buys petrol at Rs.7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of petrol if he spends Rs. 4000 each year?

• A. Rs. $7.98$
• B. Rs. $8$
• C. Rs. $8.50$
• D. Rs. $9$

Answer 1

The correct option is A Rs. $7.98$

Total quantity of petrol consumed in 3 years = $\left(\begin{array}{c}\frac{400}{7.50}+\frac{4000}{8}+\frac{4000}{8.50}\end{array}\right)$ litres
= $4000\left(\begin{array}{c}\frac{2}{15}+\frac{1}{8}\frac{2}{17}\end{array}\right)$ litres
= $\left(\begin{array}{c}\frac{76700}{51}\end{array}\right)$ litres
Total amount spent = Rs. (3 x 4000) = Rs. 12000.
$\therefore$ Average cost = Rs. $\left(\begin{array}{c}\frac{12000\times 51}{76700}\end{array}\right)$ = Rs. $\frac{6120}{767}$ = Rs. $7.98$