F consists of all outcomes that are either in E' or F (or both). In words, this consists of all outcomes whose sum is not 4 together with all outcomes whose sum is odd.
E'F consists of all outcomes that are either in E' or F (or both). In words, this consists of all outcomes whose sum is not 4 together with all outcomes whose sum is odd.
But this includes all possible outcomes other than those whose sum is 4: The ones whose sum is odd are in F, while the rest are in E'. Therefore,
F is the event that the sum of the numbers is any number other than 4.
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