…and the perimeter is equal to 2 x (length + breath)!

I visited a NGO near Vasna in Ahmedabad and got an interesting opportunity to interact with a 6th grader on the concept of ‘Perimeter’. Let’s look at our dialogue first:
 I: Do you know what is Perimeter?

He: Yes, perimeter is the outline of a shape.
 I: How can we measure the perimeter of a shape?

He: We have a formula to calculate.
 I: Can we calculate perimeter if we do not know the formula?

He: No!

I: Can we calculate the perimeter for shape 1?

He: Yes, It is easy! The formula of the perimeter is Length + Breadth + Length + Breadth. So the answer will be 5+5 + 5+5 + 4+4 + 4+4 + 5+5 + 5+5 + 4+4 + 4+4.
 I: Can you explain your answer?

He: As the formula is 2 x (Length + Breadth), we must calculate everything twice.

This brings an interesting observation to the fore; the child knew the meaning of perimeter but was so conditioned to apply the given formula that he completely ignored his own understanding of the concept and ended up getting the wrong answer.

Stick a poster on a wall or put a carpet in a drawing room, we are dealing with ‘Area’. Decorate the border of a photo frame or fencing around the kitchen garden, we are dealing with ‘perimeter’. We all, and students too, deal with measurement and area in daily life.

But what we teach in classrooms is — “Formulae”!!!

We have found that many students are not able to differentiate between perimeter as a concept and its measurement and hence for them perimeter ends up being equivalent to its formula: l +b + l +b.

Another misconception which is fairly common amongst students is that perimeter can only be calculated for shapes with straight lines. Knowledge of how kids think and why they make the mistakes they do is essential to evolve and adapt teaching methods for better understanding and learning by students.
 Happy teaching!

By Janvi Soni — Educational Specialist

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