| by Kenneth Chase | No comments

## Ex: Determine the Percent Below a Quartile Using a Box Plot

The box plots below show salaries for
construction workers and teachers. So here we have the box plot for construction workers, and the box plot for teachers. And notice
how the horizontal axis is scaled by thousands of dollars. Remember to form a box plot we use the five number summary shown here below. So by looking at our box plot, we can easily determine the minimum, the first quartile, or Q1, the median, or Q2, third quartile, or Q3, and the maximum. And these five values divide the data into four groups, where each group contains twenty-five percent of the data. So looking at our question here. If a person is making the median salary
for a construction worker, which would be here, they’re making more
than what percent of teachers? So the median
salary for a construction worker, again is here, which is thirty-five
thousand dollars per year. But notice how this value is also the
third quartile for teachers. And because this is the third
quartile for teachers, we know twenty-five percent of the date is going to be in the interval from the third quartile
to the maximum. Which means seventy-five percent of the data would be between the minimum and the third
quartile. Twenty-five percent here. Twenty-five percent here. And twenty-five percent here. So notice how a construction worker, making the median salary, is going to make more than seventy-five percent of teachers, which is our answer. I hope you found this helpful.