Answer:
34.87% probability that all 5 have a wireless device
Step-by-step explanation:
For each student, there are only two possible outcomes. Either they own a wireless device, or they do not. The probability of a student owning a wireless device is independent from other students. So we use the binomial probability distribution to solve this question.
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

In which
is the number of different combinations of x objects from a set of n elements, given by the following formula.

And p is the probability of X happening.
81% of students own a wireless device.
This means that 
If 5 students are selected at random, what is the probability that all 5 have a wireless device?
This is P(X = 5) when n = 5. So


34.87% probability that all 5 have a wireless device
It would be c
ax-5=b What you have to do is get a to be by itself
So you would add 5 to both sides:
ax-5(+5)=b(+5) = ax=b+5
And then divide x by both sides. You divide because a is multiplied by x on the left side, so to move it to the other side you’d have to do the opposite and divide:
ax /x=b+5 /x
Answer is C ... a=(b+5) /x
First rewrite as y = ..., just move the +3 to the other side (sign flips):
y = -3.
Then replace y by f(x):
f(x) = -3.
This is a straight line at y=-3.
Answer B.