Editing Divisibility rule (section)

===Divisibility by 4===
The basic rule for divisibility by 4 is that if the number formed by the last two digits in a number is divisible by 4, the original number is divisible by 4;<ref name="Pascal's-criterion"/><ref name="last-m-digits"/> this is because 100 is divisible by 4 and so adding hundreds, thousands, etc. is simply adding another number that is divisible by 4.  If any number ends in a two-digit number that is divisible by 4 (e.g. 24, 04, 08, etc.), then the whole number will be divisible by 4 regardless of what is before the last two digits.

Alternatively, one can just add half of the last digit to the penultimate digit (or the remaining number). If that number is an even natural number, the original number is divisible by 4.

Also, one can simply divide the number by 2, and then check the result to find if it is divisible by 2. If it is, the original number is divisible by 4. In addition, the result of this test is the same as the original number divided by 4.

'''Example.'''<br>
'''General rule'''
# 2092 (The original number)
# <s>20</s> <u>92</u> (Take the last two digits of the number, discarding any other digits)
# 92 ÷ 4 = 23 (Check to see if the number is divisible by 4)
# 2092 ÷ 4 = 523 (If the number that is obtained is divisible by 4, then the original number is divisible by 4)

'''Second method'''
#6174 (the original number)
# check that last digit is even, otherwise 6174 can't be divisible by 4.
# 61 <u>7</u> <u>4</u> (Separate the last 2 digits from the rest of the number)
# 4 ÷ 2 = 2 (last digit divided by 2)
# 7 + 2 = 9 (Add half of last digit to the penultimate digit)
# Since 9 isn't even, 6174 is not divisible by 4

'''Third method'''
# 1720 (The original number)
# 1720 ÷ 2 = 860 (Divide the original number by 2)
# 860 ÷ 2 = 430 (Check to see if the result is divisible by 2)
# 1720 ÷ 4 = 430 (If the result is divisible by 2, then the original number is divisible by 4)