Explanation:

Let the total amount be 200 {L.C.M of 40 and 50}

Chacobar C.P. = 200/50 = 4

Fivestar C.P = 200/40 = 5

Remaining Money after petrol = [200 - 200×10%] = 180

Remaining money after buying fivestars = [180 - 20×5] = 80

So number of Chacobar she can buy = 80/4 = 20

Hence, option 1 is the correct answer.