Sam is writing a report on cell phone usage. he collects data from a random sample of eight graders in his school, and finds that 18 out of 20 eight graders have cell phones. if there are 310 eight graders in his school, estimate the number of eighth graders who have cell phones.

step-by-step explanation:

the direct variation says that:

then the equation is of the form is given by:

            where k is the constant variation.

from the given table:

consider any value of x and m(x)=y

x = 2 and m(x)=y = 3

substitute these value in [1]; we have;

divide both sides by 2 we get;

⇒

check:

put x = -1 and m(x) = -1.5

substitute in the equation:

-1.5 = -1.5                   true

therefore, the function m(x) represents a direct variation

graph of this function as shown below: