mixture problems

Question

You need 260 mL of a 20% alcohol solution. On hand, you have a 65% alcohol mixture. How much of the 65% alcohol mixture and pure water will you need to obtain the desired solution?

Answer 1

x + y = 260

(260 mL) (20) = (x mL)(65) + (y mL)(0)

x = 80 mL of 65%

to that add 180 mL water