You need a 70% alcohol solution. 70ml of a 15% alcohol mixture. Also have 75% alcohol mixture. How much mixture will you need to add to obtain the desired solution?

Answer 1

70% ( x+ 70) = 15% * 70 + 75% x

0.7(x+ 70) = 10.5 + 0.75 x

0.7 x + 49 = 10.5 + 0.75x

49 - 10.5 = 0.75x - 0.7x

38.5 = 0.05x

3850 = 5x

x = 770

Mixes 770 ml of the 75% solution with 70 ml of the 15% solution.

The result is 75%*770 + 15%*70 = 588 = 840*.7 = 70% of 840 = 70% of (770+70)