A mixture of 150 liters of milk and water contains 20% water. How much more water should be added so that water becomes 25% of the new mixture?

Question: A mixture of 150 liters of milk and water contains 20% water. How much more water should be added so that water becomes 25% of the new mixture?

Solution:
Amount of water in the 150 liters mixture = 20% of 150
= 1/5 of 150
= 30 liters

Let,
P liters of water be added.
So, new amount of water = (30 + P)
and new total mixture = (150 + P)

ATQ,
(30 + P) = 25% of (150 + P)
⇒ 30 + P = (25/100) × (150 + P)
⇒ 30 + P = (1/4) × (150 + P)
⇒ 120 + 4P = 150 + P
⇒ 4P - P = 150 - 120
⇒ 3P = 30
∴ P = 10

∴ 10 liters more water should be added.