Pick 30 leaves from one tree. Measure each in millimetres. Plot a histogram — bars showing how many leaves fell in each length range.
Edit the data set
mean = sum/20 = 72.45median = 71.50range = 90 − 58 = 32Q1 = 66.75, Q3 = 77.50, IQR = 10.75
Measuring 30 leaves
- Pick 30 leaves from one tree, ideally at random.
- Measure each from stalk to tip in millimetres.
- Group into ranges (e.g. 50-59, 60-69 …) and draw a histogram.
- Find the mean and the middle range — most leaves cluster there.
The hump-in-the-middle shape you get is a normal-ish distribution: lots near the average, few extremes. Sample a second species and the shape shifts — that's a measurable difference.
Your turn
If the leaf lengths spread from 58 mm to 90 mm, what is the range?
What it teaches
Most leaves cluster around the average; very long and very short ones are rare. You've discovered a normal-ish distribution by hand.
Compare two trees of different species. The shapes of their distributions are different — that's how biologists tell species apart.