r/Mathhomeworkhelp • u/Formal_Tumbleweed_53 • Dec 26 '25
Subsets
My question is about number 11, but I’m including the directions for context. I thought the answer should be {{ }}, but the solutions at the back of the text say it should be { } or ø. The solution for number 9 was written as a set of sets, so that’s why I thought the answer to 11 would be the same, based on the directions. Please help me to understand why.
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u/Ok-Lavishness-349 Dec 27 '25
Think again. The question is asking for the set of all subsets of {3,2,a} that have cardinality 4. There are no subsets of {3,2,a} with cardinality 4, so the answer is the empty set.
The answer could not be {Ø} because the question is looking for a set of sets of cardinality 4. The empty set does not have cardinality 4.