Mnemonic is a word meaning memory device. The word is derived from Mnemosyne, the Greek goddess of memory and the mother of the nine Muses of Greek mythology.

For example, as a child, you probably learned the alphabet by singing a little song ("...now I've said my ABCs, tell me what you think of me."). You might have also learned to count by a little rhyme ("One, two, buckle my shoe..."). This page is devoted to mnemonics used to learn mathematics and related topics.

PRE-ALGEBRA

ORDER OF OPERATIONS

When evaluating complex expressions, we have to follow the "order of operations," which are defined to be in the following order:

Parentheses (and other symbols of inclusion);

Exponents;

Multiplication and Division, in order from left to right;

Addition and Subtraction, in order from left to right.

Using the first letters of these operations, we get PEMDAS, from which we get the most famous of all mathematical mnemonics:

Please Excuse My Dear Aunt Sally

(To find out why Aunt Sally has to be excused, click on her picture.)

ELEMENTARY SCHOOL MATHEMATICS

THE METRIC SYSTEM The basic prefixes in the metric system, from largest to smallest, are

Kilo Hecto Deka Base Deci Centi Milli

(where Base represents the base unit, such as meter, liter, gram, etc.)

Taking the first letter of each of these prefixes and using b for base unit,
we get the following sequence of letters: KHDBDCM

Now we just need to pick words that begin with these letters so as to make a sentence that will be easy to remember, the sillier the better:

Kangaroos Hop Down British Driveways Carrying M&Ms

or

King Henry Drank Both Diet Cokes Monday

or

King Henry Died By Drinking Chocolate Milk

We can also do the same sort of thing for the prefixes that represent quantities larger than the base unit. The first six such prefixes are:

Deka Hecto Kilo Mega Giga Tera

where

Deka

=

10^{1}

Hecto

=

10^{2}

Kilo

=

10^{3}

Mega

=

10^{6}

Giga

=

10^{9}

Tera

=

10^{12}

Taking the first letters again, we have DHKMGT, which gives us:

Decadent Hector Killed Meg's Gigantic Terrier

Similarly, for the prefixes going in the other direction, we have:

Deci Centi Milli Micro Nano Pico Femto Atto

where

Deci

=

10^{-1}

Centi

=

10^{-2}

Milli

=

10^{-3}

Micro

=

10^{-6}

Nano

=

10^{-9}

Pico

=

10^{-12}

Femto

=

10^{-15}

Atto

=

10^{-18}

Taking the first letters again, we have DCMMNPFA, which gives us

Darn Clever Mnemonic MakesNo PrefixForgettable, Absolutely