Your Basket 0 items - £0.00

I like to teach multiplying with negatives in a similar way to how students learned multiplication at primary school. As a quicker and more efficient form of long addition. This way students consolidate addition and subtraction with negatives and extend that to multiplication and later division.

-2 x 3 is three lots of negative two or more precisely, positive three lots of negative two.

So -2 × +3 = + -2 + -2 + -2 = -2 -2 -2 = -6

2 × -3 = – +2 – +2 – +2 = -2 -2 -2 = -6

-2 × -3 = – -2 – -2 – -2 = + 2 + 2 + 2 = +6

We work through a couple of problems this way on mini-whiteboards. I ask the students to show their working only when they need to as I’m aiming for them to naturally progress on to mental methods rather than written working. When the students generate their own rules of arithmetic as a natural progression of what they already understand they are more likely to apply that learning correctly in the future.

The less able students have a laminated number line to work on along with a timetables grid. The main learning point here is writing out the multiplication as a long addition or subtraction not necessarily being able to perform the arithmetic.

I challenge the more able students to investigate what happens when a negative is raised to an even or odd power. This continues their exploration of multiplying with negatives into index notation.

If you’re interested in teaching this lesson to your students click here to go to the lesson page.

March 10, 2019

When calculating the volume of a pyramid we can substitute the values of the length, width and perpendicular height into the formula V = 1/3 lwh. In my experience this is often provided for the students with little explanation as to why a volume of a pyramid is exactly one third the volume of a […]

March 4, 2019

When teaching solving 3D problems using trigonometry we begin the lesson with a recap of Pythagoras’ Theorem and the three trigonometric ratios. We do this by matching the ratio and equations to the respective right-angled triangle. Students are encouraged to work in pairs and to show the diagrams as part of the working out on […]

January 29, 2019

When I teach rounding to a significant figure, I ask the class to discuss in pairs or small groups a definition for the word significant. It is a word that all the students have heard before but not all are able to define. After 2 or 3 minutes of conversation I ask the students to […]