You need a 35% alcohol solution. On hand, you have a 75 mL of a 15% alcohol mixture. You also have 40% alcohol mixture. How much of the 40% mixture will you need to add to obtain the desired solution?

Answer 1

.15(75) + .4x = .35(75+x)

.4x -.35x = .35(.75)-.15(75)

.05x = .2(75)

x = .2(75)/.05 = 15/.05 = 30/.1 = 300 ml of 40%

mixed with 75 ml of 15%

yield a mixture of 300+75= 375 ml of 35%

.4(300) + .15(75)

= 120 + 11.25

= 131.25

.35(375)=131.25

40-35=5

35-15 = 20

20/5 = 4

300/75 = 4

35% is closer to 40% than to 15%, so more of 35% is needed. Exactly 4 times more

300 = 4 times 75 ml