Question

90% and 97% pure acid solutions are mixed to obtain 21 litres of 95% pure acid solution. Find the quantity of each type of acid to be mixed to form the mixture.

Answer 1

Let x litres and y litres be respectively the amount of 90% and 97% pure acid solutions.

As per the given condition

0.90x + 0.97y = 21 × 0.95

⇒ 0.90x + 0.97y = 21 × 0.95   ...(i)

And

x + y = 21

From (ii), substitute y = 21 – x in (i) to get

0.90x + 0.97(21 – x) = 21 × 0.95

⇒ 0.90x + 0.97 × 21 – 0.97x = 21 × 0.95

⇒ 0.07x = 0.97 × 21 – 21 × 0.95

⇒ `x = (21 xx 0.02)/(0.07)`

⇒ x = 6

Now, putting x = 6 in (ii), we have

6 + y = 21

⇒ y = 15

Hence, the request quantities are 6 litres and 15 litres.