Let x be the amount (the volume in milliliters) of the 5% solution to be mixed.
Then the volume of the 1% solution is 100-x milliliters.
Then your "concentration" equation is
%280.01%2A%28100-x%29+%2B+0.05%2Ax%29%2F100 = 0.02,
or, equivalently,
100-x + 5*x = 200,
which implies
4x = 100 ----> x = 100%2Fx = 25.
Answer: 25 milliliters of the 5% solution must be mised with 100-25 = 75 milliliters of the 1% solution.
