4.2.1 An Everyday Problem

Let’s suppose you purchased four large pepperoni pizzas that cost $15.99 each, and you want to split the total cost among six people evenly. To determine how much each person needs to pay, both addition and division will be used.

Fortunately, you’ve brought your calculator along, so you type it in as follows: sum with, 4 , summands 15.99 plus 15.99 plus 15.99 plus 15.99 division six. You push the “=” button or enter and the result is $50.635. Your friends aren’t going to be too pleased about that! What went wrong?

Well, you soon realize that what your calculator has done is to calculate equation sequence sum with, 4 , summands 15.99 plus 15.99 plus 15.99 plus open 15.99 division six close equals 47.97 plus 2.665 equals 50.635, because it follows the order of operations, PEMDAS. Your calculator has divided only the last $15.99, not the total, by six. What you need it to do is calculate the total first by putting it into parentheses: open sum with, 4 , summands 15.99 plus 15.99 plus 15.99 plus 15.99 close.

Now you can divide (remember, P comes before D in PEMDAS). Then, you get open sum with, 4 , summands 15.99 plus 15.99 plus 15.99 plus 15.99 close division six equals 10.66 each. Each person owes $10.66, not more than $50. Phew—much relief all around!

So you can see now how important it is to get the correct order for calculations.

4.2 Order of Operations

4.2.2 Calculator Exploration: Understanding the Order of Operations