Question 445611
x+y=19
.30x+.80y=.5(x+y)
.30x+.80y=.5x+.5y
.3y=.2x
3y=2x
2x+2y=38
3y+2y=38
5y=38
y=38/5
x=57/5
38/5 liters of coolant must be drained and replaced with 80% antifreeze to get the desired mix.  57/5 liters of 30% coolant can be left in the radiator..