Question 353498
let x = # gallons 60% antifreeze sol'n that has to be added.  Then 
{{{0.60x + 0.40*(25 - x) = 0.52*25}}},
{{{0.60x + 10 - 0.40x = 13}}},
{{{0.20x = 3}}},
{{{x = 3/0.20 = 15}}}.
Therefore 15 gallons of 60% antifreeze has to be added.