Question 1167372
This is a binomial with n=7 p=0.55 
a least 4 of them use their smartphones
that is 1-prob(3) of them use them.
=0.6083 is answer.
probability 4 use them is 7C4*0.55^4*0.45^3=0.2918 
for 5 it is 0.2140
for 6 it is 0.0872
for 7 it is 0.55^7 or 0.0152
add them to get 0.6082 (rounding error)