A 40 litre solution contains 25% salt. How many litres of water must be evaporated so that the concentration of salt becomes 40%?
Show answer & explanation
Correct answer: B
Explanation
Given:
Total solution = 40 L
Salt content = 25%
Final concentration = 40%
According to the formula:
Quantity of salt = (Percentage / 100) × Total solution
Initial salt content = (25 / 100) × 40 = 10 L
Let the amount of water evaporated be x L.
New total solution = (40 − x) L
The final concentration is 40%.
10 / (40 − x) = 40 / 100
10 / (40 − x) = 2 / 5
50 = 80 − 2x
2x = 30
x = 15
Water evaporated = 15 L