A car owner buys petrol at Rs. 17, Rs. 19 and Rs. 20 per litre for three consecutive years. Compute the average cost per litre, if he spends Rs 6460 per year.

Answer: Option B

Total quantity of petrol consumed in 3 years
= $$\left(\frac{6460}{17}+\frac{6460}{19}+\frac{6460}{20}\right)$$   litres
= (380 + 340 + 323) litres
= 1043 litres
Total amount spent
= Rs. (3 × 6460)
= Rs. 19380
∴ Average cost
= Rs. $$\left(\frac{19380}{1043}\right)$$
= Rs. 18.58