Question

A. How many ml of 10 percent acid should be added to pure acid to make 20 ml of 50 percent acid?

A) 10 ml
B) 15 ml
C) 20 ml
D) 25 ml

b. How many ml of 50 percent acid should be added to pure acid to make 40 ml of 85 percent acid?
A) 5 ml
B) 10 ml
C) 15 ml
D) 20 ml

Answer 1

To make 20 ml of 50% acid, you need to add 100 ml of 10% acid. To make 40 ml of 85% acid, you need to add 68 ml of 50% acid.

Step-by-step explanation:

To find how many ml of 10 percent acid should be added to pure acid to make 20 ml of 50 percent acid

1. Let x be the number of ml of 10 percent acid needed.
2. The amount of acid in x ml of 10 percent acid is 0.1 * x ml.
3. The amount of acid in the remaining pure acid is 20 - x ml.
4. The total amount of acid in the final solution is 0.5 * 20 ml.
5. Setting up the equation: 0.1 * x + 0 * (20-x) = 0.5 * 20
6. Simplifying: 0.1 * x = 10
7. Dividing by 0.1: x = 100

The correct answer is 100 ml (Option A).

For the second question, we can follow a similar approach.

1. Let y be the number of ml of 50 percent acid needed.
2. The amount of acid in y ml of 50 percent acid is 0.5 * y ml.
3. The amount of acid in the remaining pure acid is 40 - y ml.
4. The total amount of acid in the final solution is 0.85 * 40 ml.
5. Setting up the equation: 0.5 * y + 0 * (40-y) = 0.85 * 40
6. Simplifying: 0.5 * y = 34
7. Dividing by 0.5: y = 68

The correct answer is 68 ml (Option C).