Question

Show an equation and a solution for the problem. Arnold needs a 25% solution of nitric acid. He has 20 milliliters (ml) of a 30% solution. How many ml of a 15% solution should he add to obtain the required 25% solution?

Answer 1

Equation:
acid + acid = acid
0.30*20 + 0.15x = 0.25*(20+x)

Multiply thru by 100 to get:
30*20 + 15x = 25*20 + 25x
10x = 5*20
x = 10 ml (amt. of 15% solution needed)