Verified answer

Answer:

Step-by-step explanation:

Let x liters and y liters 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 ×0.02/ 0.07 = 6  

Now, putting x = 6 in (ii),

we have  6 + y = 21 ⇒ y = 15  

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