SOLUTION: Assume that when adults with smartphones are randomly​ selected, 57​% use them in meetings or classes. If 7 adult smartphone users are randomly​ selected, find the probabilit

This is a binomial distribution type problem, where the probability under the question is the sum


     P =       (1)


The number of trials is              7;
The indexes of success trials        k = 2,3,4,5,6,7
The probability of success trial     p = 0.57;
                                     q = 1 - p
C(n,k) = n! / (k! * (n-k)!)          are binomial coefficients.


I am going to use the Excel standard function BINOM.DIST.

It provides calculations similar sums, but only in the case, when such sums are presented in so called cumulative form
as the sums from 0 to some integer number.


Therefore, I convert the sum (1) into the cumulative form.


In cumulative form, the sum  (1)  is equal to  1 - .     (2)


Now, when the sum is presented in cumulative form, you may use the Excel function 

BINOM.DIST(1, 7, 0.57, TRUE)  to calculate 


     = 0.02794.    


In this way, the value of  (2)  is equal to  1 - 0.02794 = 0.97206 (approximately).    ANSWER