Multiplication by 9: To multiply any number by 9, simply multiply it by 10 and then subtract the original number. For example, to multiply 7 by 9, multiply 7 by 10 (70) and then subtract 7 (63).

Addition with 9: When adding a number to 9, you can use the “finger trick.” Hold up both hands with fingers extended. To add, for example, 7 to 9, put down the 7th finger from the left, and count the remaining fingers (8, 9, 10, 11, 12, 13, 14). The answer is 16.

Multiplication by 11: To multiply any two-digit number by 11, add the two digits together and place the sum in the middle. For example, to multiply 23 by 11, add 2 and 3 (5) and place it between the original digits, resulting in 253.

Counting by 2s: To count by 2s, start at any number and add 2 repeatedly. For example, starting at 3, count 3, 5, 7, 9, 11, and so on.

Counting by 5s: To count by 5s, start at any number and add 5 repeatedly. For example, starting at 10, count 10, 15, 20, 25, 30, and so on.

Counting by 10s: To count by 10s, start at any number and add 10 repeatedly. For example, starting at 4, count 4, 14, 24, 34, 44, and so on.

Addition with 0: Any number plus 0 equals the original number. This is a useful trick to remember when adding numbers.

Subtraction with 0: Any number minus 0 equals the original number. This is a useful trick to remember when subtracting numbers.

Commutative Property: Addition and multiplication can be done in any order without changing the result. For example, 2 + 3 is the same as 3 + 2, and 4 x 5 is the same as 5 x 4.

Zero Property: Any number multiplied by 0 equals 0. This is a useful trick to remember when multiplying numbers.