What makes a good mnemonic for Maths

What makes a good mnemonic for Maths

I am always looking out for mnemonics or memory tags to help in Maths. A Google or other search will generate a lot, but not so many that are useful or practical. Some have been concocted for facts that relatively few people really need to learn – for example the value of pi (roughly 3.14) to five or more decimal places – or the descent by factors of 10 of the metric measures kilo-, hecto-, deca-, metre, deci- cent- milli- King Henry Died a Miserable Death – Caught Measles – but who needs the hecto-, deca- and decimeter measures? – certainly no one at school. And the mnemonics I have seen for circle area (‘pi r-squared’) and cirumference (‘pi d’) employ rhymes that aren’t catchy – so I won’t quote them.   

Some mnemonics have of course  established themselves in textbooks – BIDMAS or PEDMAS for order of operations; SOH CAH TOA for trigonometric ratios. These acronyms don’t impose a burden on the memory, and the principles they denote are crucial.

For students who want to be able to function in Maths, but not necessarily store knowledge in it to pub quiz level, all the best mnemonics are short and simple. A good example is the mnemonic for perimeter. Vague about what it denotes? Then just remember that the perimeter is the rim . The word itself contains its meaning.

Answers to ‘harder’ multiplications should have more mnemonics of the 8×8 = 64  sort:
‘I ate and I ate and was sick on the floor – sixty four’ – or the less messy ‘ He ate and he ate ’til he stuck in the door.’ 
Here is one for 6×8:
‘Six and eight went out to skate and they came back with forty eight’ – which is nonsense, but may help some learners.

To finish, this classic children’s rhyme contains a caution on memorizing by association, but may help the more literary child with 6×9:

A Mortifying Mistake
Anna Maria Pratt
from Little Rhymes for Little People

I studied my tables over and over
And backward and forward too
But I couldn’t remember six times nine
And I didn’t know what to do
‘Til my sister told me to play with my doll
And not to bother my head
“If you call her ‘Fifty-four’ for awhile
You’ll learn it by heart’, she said.

So I took my favorite, Mary Anne,
Though I thought ’twas a dreadful shame
To give such a perfectly lovely child
Such a perfectly horrible name,
And I called her my little Fifty-four
A hundred times ’til I knew
The answer of six times nine
As well as the answer of two times two.

Next day, Elizabeth Wigglesworth,
Who always acted so proud
Said, “Six times nine is fifty-two,
And I nearly laughed out loud
But I wished I hadn’t when teacher said,
“Now Dorothy, tell if you can.”
For I thought of my doll and sakes alive!
I answered, “Mary Anne!”