There are a total of 147.7 million voters, of which 11.6 million are in the 21–24 age range. The probability a randomly selected voter is in that range is
... 11.6/147.7 ≈ 0.079 . . . p(21–24)
The probability a voter is not in that range is
... 1 - p(21–24) ≈ 0.921
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I find the question ambiguous as to what you want, so have provided numbers for both in-range and out-of-range. Use the one(s) you need.
