Here is a bar chart of the shoe sizes in a 4th Class. Look at it for a moment. Which shoe size is worn by the most pupils? And how far apart are the smallest and the biggest sizes on the chart?

Four charts on the board, each one already built. On the first, the tallest bar is the fruit chosen by the most pupils, so that value is the mode. On the pets chart, the largest is 8 and the smallest is 2, so we take 8 − 2 = 6: the range is one number you get by subtracting. Then watch for a chart where two bars reach exactly the same top height, and one where a single very tall bar stretches the spread right out.

Here is a chart of library books borrowed each day that we can explore. The daily totals are:

• Monday 8
• Tuesday 5
• Wednesday 8
• Thursday 6
• Friday 11

First, find the mode. Which value comes up more than once? Now the range. What is the smallest total, and what is the largest? Say the subtraction aloud, then check.

Today we work through four data sets, each a little trickier. For each one we find the mode and the range, and we say the subtraction aloud before we check.