Supplementary exercise 4.52 of IPS7e
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Y =  number of persons in an American household.

The probabilities sum to 1, and are all >=0, so the probability
distribution is valid.

(a) Y>1 expresses the event that more than one person lives in 
the household.

P(Y>1) = P(Y=2) + P(Y=3) + P(Y=4) + P(Y=5) + P(Y=6) + P(Y=7)
       = 0.33 + 0.16 + 0.14 + 0.06 + 0.03 + 0.01 = 0.73
or simpler
P(Y>1) = 1 - P(Y<=1) = 1 - P(Y=1) = 1 - 0.27 = 0.73

(b) P(2<Y<=4) = P(Y=3) + P(Y=4) = 0.30

(c) P(Y<>2) = 1 - P(Y=2) = 1 - 0.33 = 0.67