Question

Assume that when adults with smartphones are randomly​ selected, 49​% use them in meetings or classes. If

25 adult smartphone users are randomly​ selected, find the probability that exactly 15 of them use their smartphones in meetings or classes.

Answer 1

49% of the adults use smartphones in meetings or classes     
p = 0.49 (probability of selecting an adult who uses smartphones in meetings or classes)    
q = 1 - p = 1 - 0.49 = 0.51     
n = 25 (sample size of 25 adults selected)    
Let X be the number of adults that use smartphones in meetings or classes out of the 25 sample     
X ~ Binomial distribution with n = 25 and p = 0.49     
     
To find P(exactly 15 of them use their smartphones in meetings or classes)     
that is to find P(X =15)     
We use the Excel function BINOM.DIST to find the probability     
P(X=15)   = BINOM.DIST(15, 25, 0.49, FALSE)   (Note : Last parameter is FALSE, since we need discrete probability)  
              = 0.0877     

The probability that exactly 15 of them use their smartphones in meetings or classes = 0.0877