Multiple choice

A mixture of water and milk is $40$ litres. There is $10$% water in it. How much water should now be added in this mixture so that the new mixture contains $20$% water?

  1. $4$ litres
  2. $5$ litres
  3. $6.5$ litres
  4. $7.5$ litres
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initial water = 10% of 40 = 4L. Let x be water added. New total = 40 + x. New water = 4 + x. (4 + x) / (40 + x) = 0.2. 4 + x = 8 + 0.2x. 0.8x = 4. x = 5.

AI explanation

The initial 40 litres of mixture contains 10% water, meaning there are 4 litres of water and 36 litres of milk. Let x be the amount of water added to make the new solution 20% water; the equation becomes (4 + x) / (40 + x) = 0.20. Solving for x gives 4 + x = 8 + 0.2x, so 0.8x = 4 and x = 5. The required amount of water to add is 5 litres.