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Probabilities from frequency tables

Probabilities from frequency tables problem 2

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Jack wanted to know if taking coffee at night could really help him sleep less and study more. For several nights, Jack recorded how many cups of coffee he drank at night and how many hours he slept that night.

	6 hours	7 hours
0 cup of coffee	6	4
1 cup of coffee	5	2

If a night is chosen at random, what is the probability that it's a night when Jack took no coffee and slept for 7 hours?

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