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?

Answer 1

average cost=4000 (7.50+8+8.50)/3
=96000/3=32000

Answer 2

Total quantity of petrol consumed in 3 years =

$( \frac{4000}{7.50} + \frac{4000}{8}+ \frac{4000}{8.50})$ litres

$=4000( \frac{2}{15} + \frac{1}{8} + \frac{2}{17} )$ litres

$= ( \frac{76700}{51})$ litres

Total amount spent =Rs.(3×4000)=Rs.12000.

∴ Average cost =

$Rs. ( \frac{12000×51}{76700})=Rs.( \frac{6120}{767})$

=Rs. 7.98