Probability is (number with the characteristic) divided by (total number of teens). Where in the table do you find the total number of teens surveyed?

To get how many teens talk on a cell phone daily, look at the column total for "Talks on cell phone daily," not just one texting category.

Once you know the total number of teens and the total number who talk on a cell phone daily, place the daily-talkers count over the total number surveyed to form the probability.

In Desmos, type the fraction with the numerator equal to the column total under "Talks on cell phone daily" and the denominator equal to the grand total (799). The value Desmos outputs is the probability as a decimal; you can compare this to the answer choices written as fractions.

For equally likely outcomes, a probability is

Here, each of the 799 teens is one outcome.

Look at the bottom-right cell of the table labeled Total. This gives the total number of teens surveyed: $799$. This is the denominator of the probability.

The event we care about is "talks on a cell phone daily," regardless of texting behavior.

So we need everyone in the Talks on cell phone daily column:

• Light: 110
• Medium: 139
• Heavy: 166

The table already adds these for us in the Total row under that column: $415$ teens talk on a cell phone daily.

Now divide the number of favorable outcomes (teens who talk on a cell phone daily) by the total number of teens surveyed:

So the correct answer is $\frac{415}{799}$, which corresponds to choice B.