My Scooty gives an average of 40 km/L of petrol. But after recent filling at the new petrol pump, its average dropped to 38 km/L. I investigated and found out that it was due to adulterated petrol. Petrol pump add Kerosene, which is $$\frac{2}{3}$$ cheaper than petrol, to increase their profits. Kerosene generates excessive smoke and knocking and gives an average of 18 km per 900 ml. If I paid Rs. 30 for a liter of petrol, what was the additional amount the pump-owner was making?

Let $$x$$ ml of kerosene be there in 1 litre mixture, => Quantity of petrol in 1 litre mixture = $$(1000 - x)$$ ml

=> Required average = $$\frac{40}{1000}(1000-x)+\frac{18}{900}x=38$$

=> $$\frac{x}{25}-\frac{x}{50}=2$$

=> $$x=100$$

So, 1 litre mixture has 900 ml petrol and 100 ml kerosene.

Also, cost of 1 litre petrol = Rs. 30 and 1 litre kerosene = $$30-\frac{2}{3}\times30=Rs.$$ $$10$$

=>Actual Cost of 1 litre mixture = $$(\frac{30}{1000}\times900)+(\frac{10}{1000}\times100)$$

= $$27+1=Rs.$$ $$28$$

$$\therefore$$ Additional amount earned by pump-owner = Rs. (30-28) = Rs. 2

=> Ans - (D)