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Let x be the volume of pure antifreeze (in liters) and y be the volume of 10% antifreeze mixture (in liters).
Then you have two equations to determine x and y.
First one is
x + y = 8.
The second equation is
x + 0.1y = 0.775*(x+y).
It equalize the volume of the pure antifreeze before and after the mixing.
To solve the system, express x from the first equation, x = 8-y, and substitute it into the second equation. You will get
(8-y) + 0.1y = 0.775*((8-y) + y).
Simplify and solve:
8 - 0.9y = 0.775*8,
0.9y = 8 - 0.775*8,
0.9 y = 1.8,
y = = 2.
How many liters of pure antifreeze? 6 liters.
How many liters of 10% antifreeze? 2 liters.