Answer:
The thickness of the pile is
or 2.25 inches thick
Explanation:
Here we have from the line plot, the four thinnest books given by;
Two books of 1/2 inch thickness and two books 5/8 inch thickness
Therefore when the two 1/2 inch thick books are piled on top of the to 5/8 inch thick books we have the total thickness of the pile given as follows;

The thickness of the pile =