Divisibility Rules and Subtraction

To calculate the square root of a number

To find the largest number

To determine if a number can be divided without a remainder

To check if a number is even

Subtract the last digit from the remaining number

Double the last digit and subtract it from the remaining number

Double the last digit and add it to the remaining number

Add the last digit to the remaining number

49

50

47

48

Because 14 minus 14 equals 0

Because 14 minus 7 equals 7

Because 14 times 7 equals 98

Because 14 plus 7 equals 21

385

387

395

375

18

20

30

28

974

976

980

978

81

83

79

85

Because 81 is not divisible by 7

Because 81 is divisible by 7

Because 82 is not divisible by 7

Because 82 is divisible by 7

It is a complex method for advanced math

It only works for numbers less than 1000

It is only applicable to even numbers

It simplifies checking divisibility for any number