Shortcut Trick
Initial milk in 80 L (ratio 2:3) = 80 × (2/5) = 32 L.
Mixture replaced = 25% of 80 L = 20 L.
Milk removed = 25% of 32 L = 8 L.
Milk added = 20 L (equal to the mixture removed).
Final Milk = 32 − 8 + 20 = 44 L.
∴ The correct answer is 44 litres.
Alternate Method
Given: Total Mixture = 80 L, Ratio (M:W) = 2:3.
⇒ Initial Milk = (2/5) × 80 = 32 L.
⇒ Initial Water = (3/5) × 80 = 48 L.
⇒ Replacement amount = 25% of 80 = 20 L.
⇒ Milk in 20 L mixture = (2/5) × 20 = 8 L.
⇒ Milk left after removal = 32 − 8 = 24 L.
⇒ Milk added = 20 L.
⇒ Final amount of Milk = 24 + 20 = 44 L.
∴ The correct answer is 44 litres.
Additional Information
Mixture Replacement Rule
When a part of a mixture is replaced by one of its components, the ratio of the components in the remaining part stays the same as the original ratio.
Formula for Remaining Quantity
Remaining amount of original liquid = Initial amount × (1 − x/V)n, where x is quantity replaced, V is total volume, and n is number of operations.
Alligation in Replacement
Replacement problems can also be solved by treating the added pure component as a 100% concentration mixture.