Question

Based on a smartphone​ survey, assume that 43​% of adults with smartphones use them in theaters. In a separate survey of

211 adults with​ smartphones, it is found that 75 use them in theaters.

a. If the 43​% rate is​ correct, find the probability of getting 75 or fewer smartphone owners who use them in theaters.

b. Is the result of 75 significantly​ low?

Answer 1

Proportion, p = 0.43

Sample size, n = 211

Mean, µ = n*p = 211 * 0.43 = 90.73

Standard deviation, σ = √(n*p*(1-p)) = √(211 * 0.43 * 0.57) = 7.1914

a) Probability of getting 75 or fewer smartphone owners who use them in theaters, P(X <= 75) =

= P((X - µ)/σ <= (75 - 90.73)/7.1914)

= P(z <= -2.1873)

Using excel function:

= NORM.S.DIST(-2.1873, 1)

= 0.0144

b) Yes, it is not significantly low. As the probability is less than 0.05 so it is significantly low.