Useful Mathematics Tricks: Division, Multiplication and more

Division

• A number will be divisible by 3 if the sum of all the digits is a multiple of 3.  For example, 35,431,452 is divisible by 3 as 3 + 5 + 4 + 3 + 1 + 4 + 5 + 2 = 27 and 27 is divisible by 3.

• A number will be divisible by 4 if its last two digits is divisible by 4.  For example, 4,349,898,548 is divisible by 4 as the last two digits is 48 and 48 is divisible by 4 (Note: if the last 2 digits are 00, the number is divisible by 4 as it is a multiple of 100 and 100 is divisible by 4).

• A number will be divisible by 9 if the sum of all the digits is a multiple of 9.  For example, 53,438,652 is divisible by 9 as 5 + 3 + 4 + 3 + 8 + 6 + 5 + 2 = 36 and 36 is divisible by 9.

Multiplication

• To calculate the square of a 2-digit number ending in 5, simply multiply the first digit by the next consecutive number and put 25 as the last two digits.  For example, 25 x 25 = (2x3)25 = 625, 35 x 35 = (3x4)25 = 1225.

Prime Number Table

Below is the table of the first 30 prime numbers. You can print them out to assist your children to memorize them.

Print this table

	2	3		5		7
11		13				17		19
		23						29
31						37
41		43				47
		53						59
61						67
71		73						79
		83						89
						97
101		103				107		109
		113

Multiplication Table

Below are two multiplication tables, one in words and one in numbers.  You can print them out to assist your children to memorize them.

Print this table

Two-One Two	Three-One Three	Four-One Four	Five-One Five	Six-One Six	Seven-One Seven	Eight-One Eight	Nine-One Nine
Two-Two Four	Three-Two Six	Four-Two Eight	Five-Two Ten	Six-Two Twelve	Seven-Two Fourteen	Eight-Two Sixteen	Nine-Two Eighteen
Two-Three Six	Three-Three Nine	Four-Three Twelve	Five-Three Fifteen	Six-Three Eighteen	Seven-Three Twenty One	Eight-Three Twenty Four	Nine-Three Twenty Seven
Two-Four Eight	Three-Four Twelve	Four-Four Sixteen	Five-Four Twenty	Six-Four Twenty Four	Seven-Four Twenty Eight	Eight-Four Thirty Two	Nine-Four Thirty Six
Two-Five Ten	Three-Five Fifteen	Four-Five Twenty	Five-Five Twenty Five	Six-Five Thirty	Seven-Five Thirty Five	Eight-Five Forty	Nine-Five Forty Five
Two-Six Twelve	Three-Six Eighteen	Four-Six Twenty Four	Five-Six Thirty	Six-Six Thirty Six	Seven-Six Forty Two	Eight-Six Forty Eight	Nine-Six Fifty Four
Two-Seven Fourteen	Three-Seven Twenty One	Four-Seven Twenty Eight	Five-Seven Thirty Five	Six-Seven Forty Two	Seven-Seven Forty Nine	Eight-Seven Fifty Six	Nine-Seven Sixty Three
Two-Eight Sixteen	Three-Eight Twenty Four	Four-Eight Thirty Two	Five-Eight Forty	Six-Eight Forty Eight	Seven-Eight Fifty Six	Eight-Eight Sixty Four	Nine-Eight Seventy Two
Two-Nine Eighteen	Three-Nine Twenty Seven	Four-Nine Thirty Six	Five-Nine Forty Five	Six-Nine Fifty Four	Seven-Nine Sixty Three	Eight-Nine Seventy Two	Nine-Nine Eighty One
Two-Ten Twenty	Three-Ten Thirty	Four-Ten Forty	Five-Ten Fifty	Six-Ten Sixty	Seven-Ten Seventy	Eight-Ten Eighty	Nine-Ten Ninety

 

Print this table

2x1 = 2	3x1 = 3	4x1 = 4	5x1 = 5	6x1 = 6	7x1 = 7	8x1 = 8	9x1 = 9
2x2 = 4	3x2 = 6	4x2 = 8	5x2 = 10	6x2 = 12	7x2 = 14	8x2 = 16	9x2 = 18
2x3 = 6	3x3 = 9	4x3 = 12	5x3 = 15	6x3 = 18	7x3 = 21	8x3 = 24	9x3 = 27
2x4 = 8	3x4 = 12	4x4 = 16	5x4 = 20	6x4 = 24	7x4 = 28	8x4 = 32	9x4 = 36
2x5 = 10	3x5 = 15	4x5 = 20	5x5 = 25	6x5 = 30	7x5 = 35	8x5 = 40	9x5 = 45
2x6 = 12	3x6 = 18	4x6 = 24	5x6 = 30	6x6 = 36	7x6 = 42	8x6 = 48	9x6 = 54
2x7 = 14	3x7 = 21	4x7 = 28	5x7 = 35	6x7 = 42	7x7 = 49	8x7 = 56	9x7 = 63
2x8 = 16	3x8 = 24	4x8 = 32	5x8 = 40	6x8 = 48	7x8 = 56	8x8 = 64	9x8 = 72
2x9 = 18	3x9 = 27	4x9 = 36	5x9 = 45	6x9 = 54	7x9 = 63	8x9 = 72	9x9 = 81
2x10 = 20	3x10 = 30	4x10 = 40	5x10 = 50	6x10 = 60	7x10 = 70	8x10 = 80	9x10 = 90