4.2.4 Moving Left to Right
There is one other point to note about using the PEMDAS code. Division is the opposite of multiplication; it “undoes” multiplication. If you multiply by three and then divide by three, you end up where you began. So, although multiplication comes before division in the PEMDAS code, they are really on the same priority level. The same is true of addition and subtraction: Because subtraction is the opposite of addition, addition and subtraction are on the same level. Therefore, we have an addendum to the PEMDAS code:
Let’s see how this works.
Suppose that you are trying to calculate . There is a subtraction and an addition; these are at the same level, so work from left to right.
Luckily the calculator knows about this aspect of the PEMDAS code and will automatically follow it.
The calculator can be accessed in the left-hand side bar under Toolkit.
Activity: More on PEMDAS
Here are a couple more calculations to make sure that you have things straight. Try them without the calculator, and then use the calculator to check your answer.
Start by thinking through PEMDAS code. If you find more than one calculation at the same priority level, work through them from left to right.
Parentheses come first, but in the second set of parentheses, there is an addition followed by a subtraction. These are on the same level so when you do that calculation, work from left to right.
and , so
Inside the parentheses, there is a subtraction operation followed by an addition operation. Because addition and subtraction have the same priority level, you will work from left to right, so
Now there is a multiplication and a division, so again, you’ll work from left to right:
Make sure that you have added PEMDAS to your math notebook so that you can refer back to it easily if you need a reminder.
Now you have the hang of the basics try the activity on the next page. It’s a brainstretcher so don’t feel bad if you need to use the hints for help!