Question 258552
A photographer is mixing 2 liters of a 10% acetic acid solution with a 5% solution to get a 7% solution.
Let x liters of the 5% solution he add.
Then,   2*(10/100)+x*(5/100) = (2+x)*(7/100)
        20+5x = 14+7x
        20-14 = 7x-5x
        6 = 2x
        2x = 6
        x = 3