90% and 97% pure acid solutions are mixed to obtain 21 litres of 95% pure acid solution. Find the quantity of each type of acids to be mixed to form the mixture.
Let the quantity of 90% acid solution be x litres.
∴ quantity of 97% acid solution = (21 - x) litres
Now,
90% of x + 97% of (21 - x) = 95% of 21
⇒ 7x = 21(97 - 95)
⇒ 7x = 42
⇒ x = 6
Thus, 90% acid solution = 6 litres
97% acid solution = 21 - 6 = 15 litres
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