Answer: Choice A) Set W is all the unique three-digit numbers using the digits 1, 3, and 5
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Explanation:
The original set uses the digits {1,2,3,4,5}. We can only use those digits. Nothing else. So that means we can't use 0, 2, 4, 6, or 7. This rules out choices B through D.
Only choice A is left. This answer choice involves 1,3 and 5 which is the correct subset of digits to use.
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Put another way, if set B was a subset of set A, then everything in B must also be found in A. Having B = {2,4,6} and A = {1,2,3,4,5} shows B is not a subset of A. We see a counter example has 6 in B, but not in set A.
This allows us to rule out choice B. Similar ideas apply to the answer choices C and D as well.
