A 90-litre mixture of petrol and kerosene is in the ratio 4:5. Some of it is removed and replaced with pure petrol. The final ratio becomes 7:5. How much of the mixture was replaced?
Show answer & explanation
Correct answer: B
Explanation
Initial mixture = Petrol : Kerosene = 4 : 5
Petrol = 40 liters
Kerosene = 50 liters
Let x liters of the mixture be withdrawn.
In the withdrawn mixture,
Petrol = 4x/9
Kerosene = 5x/9
x liters of pure petrol were added.
Therefore, new petrol = 40 − 4x/9 + x
= 40 + 5x/9
New kerosene = 50 − 5x/9
(40 + 5x/9) / (50 − 5x/9) = 7/5
5(40 + 5x/9) = 7(50 − 5x/9)
1800 + 25x = 3150 − 35x
60x = 1350
x = 22.5 liters