The graph compares shoe sizes for a group of 120 two-year-old boys and a group of 60 three-year-old boys. Two box and whisker plots showing shoes sizes on a number line from 2.5 to 13. The upper plot represents the group of 2 year-old boys. For this upper plot, the minimum number is 3, the maximum number is 9.5, the right side of the box is 7.5, the left side of the box is 3.5, and the bar in the box is at 6. The lower plot represents the group of 3 year-old boys. For this lower plot, the minimum number is 5, the maximum number is 11.5, the right side of the box is 9.5, the left side of the box is 6.5, and the bar in the box is at 8. About how many more two-year-old boys have a shoe size of 6 or less, compared to the three-year-old boys?

There are about 45 more 2 year olds with a shoe size of 6 or less than 3 year olds with a shoe size of 6 or less.

The median of the two year old box plot, the bar in the middle, is at 6.  This means this is the halfway point of the data; half of the data will be above it, half below it.  There are 120 2-year-olds; 120/2 = 60.  This means there are 60 with that shoe size or smaller.

The lower quartile of the three year old box plot, the bar that makes the left side of the box, is at 6.5.  This is the middle of the lower half of data; 1/4 of the data is from this point below, and 3/4 of the data is from this point above.  There are 60 3-year-olds; 60/4 = 15.

The difference between the two is given by
60 - 15 = 45