Amixture of 6% disinfectant solution is to be made from 8% and 3% disinfectant solutions. how much of each solution should be used if 25 gallons of 6% solution are needed?

Answer is: 10 gallons of 3% and 15 gallons of 8% solution.
V₁ + V₂ = 25 gallons.
0,03V₁ + 0,08V₂ = 0,06 · 25 gallons.
V₁ = 25 gallons - V₂.
0,03 · (25 gallons - V₂) + 0,08V₂ = 1,5 gallons.
0,75 gallons - 0,03V₂ + 0,08V₂ = 1,5 gallons.
0,05V₂ = 0,75 gallons.
V₂ = 0,75 gallons / 0,05.
V₂ = 15 gallons.
V₁ = 25 gallons - 15 gallons.
V₁ = 10 gallons.

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