Correct Answer - Option 4 : 5∶9

**Given∶**

CNG car gives an average that is 20% higher than petrol car.

Also, petrol costs 50% of its price higher than CNG.

**Formula Used∶**

Simple concept of Percentage and Ratio.

**Calculation∶**

Let the Mr. Y's petrol car covers a distance of 100 km in per liter.

Then, Mr. X's CNG car covers a distance of 120 km in per liter.

Let the cost of CNG per litre = Rs. 100

then, the cost of petrol per liter = Rs. 150

now, cost per liter of Mr. Y's car = 100/150 = 2/3

Also, cost per liter of Mr. X's car = 120/100 = 6/5

Required ratio = 2/3 ∶ 6/5 = 5 ∶ 9

**∴ The ratio of cost per kilometer of Mr. Y's car to Mr. X's car is 5∶9.**