Adding 600 g water to 400 g of 20% brine

There are 400 g of brine at 20% concentration. After 600 g of water is added, the total becomes 1000 g. What is the concentration of the diluted brine?

Step-by-step

1. 20% × 400 = 80
   Mass of solute (unchanged by adding water or evaporating)
2. 80 ÷ 1000 = 8%
   Solute ÷ new total solution = new concentration

Why it works

Adding water increases the total mass but leaves the amount of salt unchanged, so the new concentration is the same salt divided by the larger total mass.

Common mistakes

• Dividing the salt by the original 400 g instead of the new total.
• Subtracting the water from the concentration.

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