You need a 40% alcohol solution. On hand, you have a 245 mL of a 35% alcohol mixture. You also have 75% alcohol mixture.

Question

You need a 40% alcohol solution. On hand, you have a 245 mL of a 35% alcohol mixture. You also have 75% alcohol mixture. How much of the 75% mixture will you need to add to obtain the desired solution?

Answer 1

.35(245) + .75x = .4(245+x) = 98 + .4x

85.75 + .75x = 98 + .4x

.35x = 98-85.75 = 12.25

x = 12.25/.35 = 35 mL of 75% solution

mixed with 245 mL of 35% yields 280 mL of 40%

35 is within 5 of 40

75 is within 35 of 40

35/5 = 7

245/35 = 7