Answer:
55 from un-pure and 165 from pure
Step-by-step explanation:
to get 220 pints with 95% purity you need a mixture of 209 parts to 11 parts (220 *0.95 and 220 * 0.05)
we call the un-pure mixture a and the pure mixture b
all un-pure parts come from a and b in the following ratios
11 = 0.2a + 0b (each pint of mixture a adds 0.2 pints of unpure stuff and each pint of b adds no unpure stuff)
which we can then solve as:
a = 55
all pure parts come from a and b in the following rations
209 = 0.8a + 1b (each pint of mixture a adds 0.8 pints of pure stuff and each pint of b adds a full pint of the pure stuff)
now we can replace a with 55 (from above)
209 = 44 + b, and solve to
b = 165
now to double check
55 * (0.8x + 0.2y) + 165x would give you
44x + 11y + 165x, which is
11x + 209y and if you then check the ratio
209 / (209+11) = 0.95 again
