Exercise 1 Page 374

We will begin by looking at the two-way table that shows the result of a survey that asked the students in our grade whether they have a cell phone.

Our friend claims that a greater percentage of males in our grade have cell phones than females. To find out if our friend is correct, let's first calculate the marginal frequencies for the two-way table. A marginal frequency is the sum of the row or column of joint frequencies in a two-way table. Each entry in the table is a joint frequency. Let's find the marginal frequencies.

We can now use conditional relative frequencies to determine whether our friend is correct. The conditional relative frequency is the ratio of a joint frequency and either of its corresponding marginal frequencies. In this case, we must use conditional relative frequencies based on row totals.

Let's simplify the ratios.

From the table, we can see that about $69\%$ of males have cell phones. Conversely, about $65\%$ of females have cell phones. Therefore, our friend's claim that a greater percent of males in our grade have cell phones than females is correct.