Friday, July 26, 2013

Welcome to Maths. Please leave your common sense at the door

I come across many students who feel that it is unacceptable to solve a Maths problem on first principles. They always go searching for a formula and, when none can be found, give up on the problem. In this blog post, I give two examples to illustrate this phenomenon.

What is five percent of 100?
Last term, I put a question to my year 7 class which involved calculating 5% of $250? We had not covered percentages yet and I wanted to see how they would approach this. Some students had little difficulty with the calculation although the majority decided they couldn't do percentages. Some tried to remembered a formula they had learnt earlier.
Mr Baroudi, do you multiply by 100 over 1 or do you divide by 100 over 1?

I told them not to worry about any formal methods for the time being. Instead, I asked them, "What does 'per cent' mean?" Everyone seemed to know it meant "out of 100".
I drew the diagram below, one step at a time, asking them, "How much will we take out of this $100 (or $50)"?
What is 5% of $250?