“When these comments are made in the classroom I ask the students to take out their calculators. I get them to tap the buttons as I give them a problem. “Two plus three times four equals…?”

Some students get 20 as an answer on their calculator. Others get an answer of 14.

Which number is correct? How can calculators give two different answers when you press the same buttons?

This is because there is an order of mathematical functions. You multiply and divide before you add or subtract. Some calculators know this; some don't.

A calculator can't think for you. You must understand what you are doing yourself. If you don't understand mathematics, a calculator is of little help.”