A hair dye is made by blending 7% hydrogen peroxide solution and 4% hydrogen peroxide solution. How many milliliters are used of each to make a 300mL of 5% solution.

Question

All help is appreciated!

Answer 1

(x ml)(7%) + (300 - x ml)(4%) = (300 ml)(5%)

7x + 1200 - 4x = 1500

3x = 300

x = 100 mls of 7%

300 ml - 100 ml = 200 mls of 4%

Done by alligation:

HAVE.........WANT..........NEED

4%...................................2 parts

.................5%............................

7%..................................1 part

Total parts = 3 = 300 ml, so each part = 100 ml

2 parts of 4% = 200 mls of 4%

1 part of 7% = 100 mls of 7%