Opposite Math

 

Hot . . . Cold

Wet . . . Dry

New . . . Old

Open . . . Shut

Children can grasp the idea of opposites at a young age. If you take advantage of this concept when teaching math, it cuts your work in half!

Instead of teaching subtraction, teach “opposite addition”. If you know that 3 + 5 = 8, then you can do the opposite. When you see this problem: 8 – 5 =___, just make it into a backwards addition problem. Start at the opposite end (the back) and add this way: what number plus 5 equals 8 ?

This works for multiplication too. Once you know your times tables*, then division is a snap! If you know that 4 x 6 = 24, then “opposite multiplication” will solve 24 divided by 6 = ___ . Start at the opposite end (back) of the problem to read it: what number times 6 equals 24?

The most fun application of opposite math is in dividing fractions. This may look like a formidable problem to kids:

(I know that it stumps me briefly when I cook and have to divide a recipe.) But if you teach them that division is just “opposite multiplication”, then you can turn the second fraction upside down (into its reciprocal), and make this into an easy multiplication problem:

Now it’s easy to divide fractions. Just let opposites do the work!

Have a good math day!

 

*If you want some excellent help teaching math facts, take a look at Math It, my very favorite “math facts” product. It gives children a reason and memory clues, rather than just requiring rote memorization of the addition and multiplication facts. Great stuff!

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