UPSC Civil Services 2015 Prelims General Studies Paper II

Let number of cars be x
Let number of scooters / motor bikes = y
∴ Total number of parked vehicles = x + y
According to question
4x + 2y = 2 (x + y) + 100
4x + 2y = 2 x + 2y + 100
2x = 100
x = 50
Hence, Number of cars parked is 50.