Mixture Question 3

Question

You need 180 mL of a 75% alcohol solution. On hand, you have a 70% alcohol mixture. How much of the 70% alcohol mixture and pure alcohol will you need to obtain the desired solution?

Answer 1

70(180-x) + 100x = 75(180) x is the amount of pure alcohol needed

30x = 75(180)-70(180) = 5(180)

6x = 180

x = 30 mL of pure alcohol

180-x = the amount of 70% alcohol needed= 150 mL

150= 5 times 30

70 is 5 times closer to 75 than 75 is to 100

75-70=5

100-75= 25

5 times 5 = 25