Blend of 10% and 30% brine

300 g of brine at 10% concentration is combined with 200 g of brine at 30% concentration. What is the concentration of the blend?

Step-by-step

1. 300 × 10% = 30
   Solute in this portion
2. 200 × 30% = 60
   Solute in this portion
3. 30 + 60 = 90
   Total solute is unchanged during mixing
4. 90 ÷ 500 = 18%
   Concentration = solute ÷ total solution

Why it works

Salt is conserved when solutions are combined: the total salt is the sum of each part's mass times its concentration, and the new concentration is that salt divided by the total mass.

Common mistakes

• Averaging 10% and 30% without allowing for the different masses.
• Dividing the total salt by only one of the two masses.

Related

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