Question 892529
Let x = the # of liters to be drained and replaced.
After drainage, there is 8 - x liters left, with 25% antifreeze.  The amount x liters is 100% antifreeze. The resulting 8 liters of solution has 66% antifreeze.
Hence 0.25*(8 - x) +1.00x = 0.66*8
==> 2- 0.25x + x = 5.28
==> 0.75x = 3.28
==> x = 3.28/0.75
+==> x = 4.37 liters of pure antrifreeze