Students can quickly memorize multiplication facts for numbers multiplied by five. Any even number, when multiplied by five, will end in zero. Any higher number multiplied by five will end in five. When multiplying any number by 10, the student quickly learns the answer is obtained by simply adding a zero to the existing number.
The answer to every math problem, when a number is multiplied by any even number, is an even number. Regardless of the first number in the equation, any number multiplied by an even number will produce an even number for the answer.
When any number is multiplied by three or nine, the correct answer will fit into this fun number trick. When the two digits in the answer are added together, their sum is also divisible by three or nine. For example: 7 x 3 = 21. Add together the 2 and 1 from 21: 2 + 1 = 3. This new answer is also divisible by three. Here is another example: 8 x 9 = 72. Add together the 7 and 2 from the answer, 7+2=9, and the answer is also divisible by both nine and three.
When introducing multiplication, students grasp the concept quickly once they realize that multiplication is the successive addition of numbers. For example: 5 x 6 is the same as 5 + 5 + 5 + 5 + 5 + 5. For some students being introduced to multiplication, this simple memory aid helps them gain traction, as they seek to calculate and memorize their math facts, because they are building on addition which they already know.
When students are taught math facts that include the use of simple mnemonic devices, they are free to focus on math facts that offer no such mnemonic devices and must be memorized. For most students, memorizing math facts from one through six is relatively simple. Math facts that include the sevens, eights and nines are less familiar to elementary school students and take more time to memorize. In the same way business managers devise their schedules to manage by exception, students who understand the mnemonic devices can focus their attention on the exceptions to the rules.