Question 298146
10x + 15(100-x) = 12(100)

10x + 1500 - 15x = 1200
-5x + 300 = 0 
Add 5x to each side:
300 = 5x
divide both sides by 5 
{{{ 300/5 = 5x/5 }}} so 60 = x <br>
x = 60 ml of the 10% solution & bob's your uncle!