Assume that when adults with smartphones are randomly selected, 35% use them in meeting or classes. if 7 adults smartphones users are randomly selected, find the probability that exactly 4 of them use their smartphones in meeting or classes.

The probability is

This is a binomial probability problem

p = 0.35 = chance of picking 1 person who uses smartphones during meeting/class

n = 7 = sample size

k = 4 = target number of people who use their smartphone

Compute nCk = 7C4 using the nCr combination formula

nCr = (n!) / (r! * (n-r) !)

7C4 = (7!) / (4! * (7-4) !)

7C4 = (7*6*5*4!) / (4!*3!)

7C4 = (7*6*5) / (3!)

7C4 = (210) / (6)

7C4 = 35

Use this coefficient to find the binomial probability

B (k) = binomial probability for input k

B (k) = (nCk) * (p^k) * (1-p) ^ (n-k)

B (4) = (7C4) * (0.35^4) * (1-0.35) ^ (7-4)

B (4) = 35 * (0.35^4) * (0.65) ^3

B (4) = 0.144238

So the approximate answer is 0.144238

This value is accurate to 6 decimal places