Skill: Estimate perimeter

Perimeter is the approximate distance around the outside of a figure. It is different from area, which measures the space inside a figure.

To estimate a perimeter:

1. Identify the lengths of the outside sides.
2. Round each measurement to a convenient number.
3. Add the rounded side lengths.
4. Include the correct unit.

Example: A rectangular garden is $12.4\text{ m}$ long and $7.8\text{ m}$ wide. Estimate its perimeter.

Because opposite sides of a rectangle are equal, the garden has two sides that are about $12.4\text{ m}$ and two sides that are about $7.8\text{ m}$.

Round the measurements:

$$12.4\text{ m} \approx 12\text{ m}$$ $$7.8\text{ m} \approx 8\text{ m}$$

Now add all four estimated sides:

$$12+8+12+8=40$$

So, the estimated perimeter is

$$\boxed{40\text{ m}}$$

The garden’s perimeter is about $40$ meters.