Box & Whisker Plots Examples Page 2

Answer the following questions, based on these box plots, on the amount of time boys and girls spend per day on social networking sites.

Approximate the girls' IQR and the boys' IQR.

a) The girls' lower quartile is about 1.25 hr/day and the upper quartile is about 3.5 hr/day.
The boys' lower quartile is about 0.6 hr/day and the upper quartile is about 1.35 hr/day.

Girls' IQR = 3.5 – 1.25 = 2.25 hours/day
Boys' IQR = 1.35 – 0.6 = 0.75 hours/day

What percentage of girls spend more than 1.25 hours/day on these sites?

1.25 hr/day is the lower quartile, so three sections of the plot are greater than Q1. Each section has 25% of the data, so 75% of the girls spend more than 1.5 hr/day.

What percentage of boys spend more than 1.35 hours/day on these sites?

1.35 hr/day is the upper quartile, so one section of the plot are greater than Q3. Each section has 25% of the data, so 25% of the boys spend more than 1.35 hr/day.

If one girl spends 6 hours/day on MyBook and FaceSpace, would she be considered an outlier?

If 6 hours/day is an outlier it will be more than 1.5(IQR) greater than Q3. The girls' IQR is 2.25 hr/day. The upper quartile is 3.5. 

1.5(2.25) + 3.5 = 6.875 hr/day

6 hr/day is not greater than this, so it isn't an outlier.