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169. $A$ is a necessary condition for $B$. Formulate a sufficient condition for the negation of $B$.

This one wants a proof. Work it on paper, read the official solution, then mark yourself honestly — the ladder only means something if the record is true.

I solved it I didn't Skip

Official solution

169. For $B$ to be false, it is sufficient that $A$ is false.

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.