Luke Z.

The probability that an individual is right-handed is 0.90. In a class of 25 students, find the probability that...

(Let X = number of individuals who are right-handed)

a. 22 students are right-handed

b. at most 23 students are right-handed

By: Robert C.

tutor
On part (b), the event that X is at most 23 is equivalent to the event that X >= 0 and X <= 23. The complement of this event is the event that 24 <= X <= 25 or simply X = 24 or X = 25. These events are mutually exclusive, thus the probability P(X = 24 or X = 25) = P(X = 24) + P(X = 25). Determine each of the two probabilities using the binomial probability formula. Then sum the two probabilities and subtract the result from 1. This should yield the answer to part (b).
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03/02/20 Robert C.

tutor
Note on probability of complement: Given event E, the probability of the complement of E (call it EC) is given by P(EC) = 1 - P(E).
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03/02/20

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