Step 2 Suppose we wish to have 7 class intervals, then the interval width is 3.5|( range)7≈0.5 So we choose 0.5 as the interval width Department of Health StatisticsSuppose we wish to have 7 class intervals, then the interval width is 3.51(range)/7 ≈ 0.5 So we choose 0.5 as the interval width . Department of Health Statistics Step 2