Question

A pharmacist has a 12% solution of boric acid and a 20% solution of boric acid. How much of each must he use to make 80 grams of a 15% boric acid solution

Answer 1

Answer:

• He must use 50g of the 12% solution and 30 g of the 20% solution.

Explanation:

Call x the amount of 12% boric acid solution to be used.

• The content of acid of that is: 0.12x

Since he wants to make 80 grams of solution, the amount of 20% boric acid solution to be used is 80 - x.

• The content of acid of that is{ 0.20(80 - x).

The final solution is 15% concentrated.

• The content of boric acid of that is 0.15 × 80 g.

Now you have can write your equation:

         $0.12x+0.20(80-x)=0.15\times 80$

Solve:

           $0.12x + 16 - 0.20x=12\\\\-0.08x=12-16\\\\0.08x=4\\\\x=4/0.08\\\\x=50$

That is 50 grams of the 12% solution of boric acid.

Calculate the amount of the 20% solution of boric acid:

         $80-x=80-50=30$

That is 30 grams.

Then, he must use 50g of the 12% solution and 30 g of the 20% solution.