By mixing 40% and 15% solutions of the same substance, a 20% solution was obtained. How many times took more by weight of a 15% solution than a 40%?
let the mass of a 15% solution be n times greater, then
m is the mass of a 40% solution, and n * m is the mass of a 15% solution, then
0.4m + 0.15 * (n * m) = 0.20 * (m + n * m)
0.4 + 0.15n = 0.20 + 0.20n
0.05n = 0.2
n = 4
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