How many liters of 15 acid and 33 acid should be mixed to make 40 liters of 21 acid solution answer key?

Answer is: 26.67 liters of 15% acid and 13.33 liters of 33% acid are needed.

ω₁ (acid) = 15% = 0,15.

ω₂ (acid) = 33% = 0,33.

V₁ (acid) = ?

V₂ (acid) = ?

V₃ (acid) = 40l.

ω₃ (acid) = 21% = 0,21

1) V₁ + V₂ = 40l, V₁ = 40 - V₂.

2) 0,15·V₁ + 0,33·V₂ : 40 = 0,21

0,15· (40 - V₂) + 0,33·V₂ : 40 = 0,21

6 - 0,15V₂ + 0,33V₂ : 40 = 0,21.

0,18V₂ = 2,4, V₂ = 13,33l.

V₁ = 40 - 13,33 = 26,67l.