An empty fuel tank of a car was filled with A type petrol. When tank was half-empty, it was filled with B type petrol. Again when tank was half-empty, it was filled with A type petrol. When tank was half-empty again, it was filled with B type petrol. What is percentage of A type petrol at present in tank?

Let the capacity of the tank be 100 litres
Initially: A type petrol = 100 litres

After first operation:
A type petrol = $$\frac{{100}}{2}$$ = 50 litres
B type petrol = 50 litres

After second operation:
A type petrol = $$\frac{{50}}{2}$$ + 50 = 75 litres
B type petrol = $$\frac{{50}}{2}$$ = 25 litres

After third operation:
A type petrol = $$\frac{{75}}{2}$$ = 37.5 litres
B type petrol = $$\frac{{25}}{2}$$ + 50 = 62.5 litres
Required percentage = 37.5%