Monthly Archives: September 2014

The Order of Operations…where we always begin

When I was in high school I felt like every science class began with the scientific method. There was that one glorious week when pencils were sharpened, notebooks color coded, and the hopes for the year were oh so high. The first lunch at co-op would be a great one and in science class we would review the scientific method…that was what I came to count on.

In math class and equally predictable lesson 1.1 came every year…the order of operations. No matter how great or modest the math class for that particular year, Dear Aunt Sally always needed to be excused before we could go any farther.

But now that I am on the other side of the desk (figuratively speaking) I still begin each class with a quick review of the rules that all mathematicians have agreed upon for the simple reason that kids continue to forget them. Take this problem for example.

Evaluate the expression.
10\div 2\cdot 5

I have had many a student tell me quite adamantly that the answer is 1 when it is in fact 25 because we perform multiplication and division together from left to right. Or take this problem….

Evaluate the expression.
(3^2-15\cdot 2\div 3)-(5^2\div 5)

Most students correctly evaluate everything until they get to the final step . The sight of that many negative signs at once makes people go crazy 🙁

So at the beginning of this school year take a moment to sit down with Dear Aunt Sally and quickly review the agreed upon order of operations. Otherwise it will just come back to haunt you later on.