How many quarts of pure antifreeze must be added to 9 quartz of a 40% antifreeze solution to obtain a 60% antifreeze solution?

Answer 1

If 9 quarts has 40% of pure antifreeze, we have X quarts of pure antifreeze = 9 / 0.4 = 3.6 quarts.

If we add Y quarts of pure antifreeze (X + Y), we have 60% solution with quantity of (9 + Y) quarts. It gives us

X + Y = (9 + Y) x 0.6

3.6 + Y = 5.4 + 0.6Y

Y - 0.6Y = 5.4 + 3.6

0.4Y = 1.8

Y = 4.5

Answer: We have to add 4.5 quarts of pure antifreeze.

Additional explanation: : total of X + Y = 3.6 + 4.5 = 8.1 quarts of pure antifreeze, 8.1 is just 60% of final solution, total we have 13.5 quarts of 60% solution of antifreeze.

Answer 2

x100+9:40

————— =60x+60y

x+y -40x-9y

————

20x=51y

x=51

y=20 quarts/71%