Test your GRE Quant concepts - August 1, 2022

I am unable to understand why won’t we take independent case here? one case would be mutually exclusive, another case would be complete overlap but why not independent case? In the solution video Greg said we won’t take independent case here because we are setting up extremes but question doesn’t mention anything like this.

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“M or N” means “M + N - Both” right?

So one extreme is mutually exclusive, the other is complete dependence. Independent sits somewhere in between.