The perimeter of a square is 40 metres. What is the length of one side of the square?

Introduction:
This is a very basic geometry problem that tests understanding of the relationship between the perimeter and side length of a square. The perimeter of a square is four times the length of one side because all four sides are equal. Once the perimeter is given, finding the side length is a simple division problem.

Given Data / Assumptions:

• The figure is a square. • Perimeter of the square = 40 metres. • All four sides of a square are equal in length. • Let the length of one side be s metres.

Concept / Approach:
The perimeter P of a square is given by P = 4 * s, where s is the side length. To find s from a known perimeter, we simply rearrange the formula to s = P / 4. This direct relationship makes these problems quick to solve once the formula is remembered.

Step-by-Step Solution:
Step 1: Write the formula for the perimeter of a square. P = 4 * s. Step 2: Substitute the given perimeter P = 40 m. 40 = 4 * s. Step 3: Solve for s. s = 40 / 4 = 10. Step 4: Interpret the result. The length of one side of the square is 10 metres.

Verification / Alternative check:
We can check quickly by multiplying the side back by 4. If side s = 10 m, then perimeter = 4 * 10 = 40 m, which is exactly the given value. This confirms that the side calculation is correct and consistent with the perimeter definition.

Why Other Options Are Wrong:
Option 20 m: This would give a perimeter of 4 * 20 = 80 m, which is double the given perimeter. Option 30 m: This would produce a perimeter of 4 * 30 = 120 m, far larger than required. Option 40 m: This would make the perimeter 4 * 40 = 160 m, four times the given value. Option 5 m: This would give a perimeter of 4 * 5 = 20 m, only half of the given perimeter.

Common Pitfalls:
The most common mistake is to divide by 2 instead of 4, confusing the formula for the perimeter of a square with that of some other figure. Another minor error can be misreading the units, but here the units are consistent. Remembering that a square has four equal sides and that perimeter is the sum of all sides helps avoid confusion.

Final Answer:
The length of one side of the square is 10 metres.