The proportion
peanuts : raisins : chocolate chips = 4 : 6 : 2
tells you that peanuts make up
4/(4+6+2) = 1/3
of the total quantity of the mix.
The quantity of peanuts required is (1/3)*(48 ounces) = 16 ounces (or 1 pound).
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In the 48 ounces of mix, 1 part = 4 ounces.