Predict the result
Calculate twenty one minus four times thirteen.
Which operation comes first?

Set up the model
In this expression, multiply before subtracting.
Four times thirteen equals fifty two. Keep the twenty one and its subtraction sign in place.

Work the example
Replace the product by fifty two. Twenty one minus fifty two equals negative thirty one.
The original expression equals negative thirty one.
Multiplication comes before subtraction here, even though subtraction is written first.

Check the result
Now calculate forty three plus eighteen times fifteen.
Multiply first, then add. Take eight seconds to think.
[Eight-second silent pause to work; the answer remains hidden.]
Eighteen times fifteen is two hundred seventy. Now add forty three and two hundred seventy.
Add to get three hundred thirteen.

Interpret the result
After grouping and exponents, multiply and divide from left to right.
Then add and subtract from left to right.
Multiplication and division have equal priority. Addition and subtraction also have equal priority.