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Assume that when adults with smartphones are randomly​ selected, 51 ​% use them in meetings or...

Assume that when adults with smartphones are randomly​ selected, 51 ​% use them in meetings or classes. If 9 adult smartphone users are randomly​ selected, find the probability that at least 2 of them use their smartphones in meetings or classes.

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Answer #1

Let X be number of adults who use their smartphones in meetings or classes.

Here, X ~ Binomial ( n = 9, p = 0.51)

probability mass function of X is,

P(X = x) = nCx px (1-p)n-x

We want to find, P(X >= 2)

P(X>=2)

= 1 - P(X < 2)

= 1 - [ P(X = 0) + P(X = 1) ]

= 1 - [ 9C0 * (0.51)0 * (0.49)9 + 9C1 * (0.51)1 * (0.49)8 ]

= 1 - [ 1 * 1 * (0.49)9 + 9 * (0.51) * (0.49)8 ]

= 1 - [ 0.0016 + 0.0153 ]

= 1 - 0.0169

= 0.9831

=> P(X >= 2) = 0.9831

Therefore, the probability that at least 2 of them use their smartphones in meetings or classes is 0.9831

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