hi and welcome to divisibility rules - in this video you'll learn the
divisibility rules for three six nine and twelve these rules let you know at
first glance if a number can be divided by another number and it makes long
division and doing math in your head a lot easier you can learn more about
divisibility rules by watching the divisibility rules one video so let's
get started we're gonna start with the divisibility rule for the digit 3 and to
find this rule we just have to add up the numbers and the dividend and
remember the dividend is the number that you're dividing into and see if that
number is divisible by 3 this is pretty confusing so let's do an example
141 divided by 3 we add up the numbers 1 4 & 1 which is 6 and since we know that
6 is divisible by 3 that means 141 must be divisible by 3 the rule for the digit
6 is a little bit more complicated basically you combine the rules for 3 &
2 this means that the last number of the digit has to be even and the sum of the
digits and the dividend have to be divisible by 3 let's do some examples
let's break this down to check if it works for both rules
four divided by two equals to 4 is divisible by 2 therefore 114 is
divisible by 2
one plus one plus four equals six 6 divided by 3 equals 2 6 is divisible by
3 therefore 114 is divisible by 3
since 114 is divisible by 3 and 2 we know that it is also divisible by 6
now let's look at another example 344 again the last digit is even so it
passes that but when we add them up for four and
three it's 11 which is not divisible by three even though it passes one rule if
it doesn't pass both rules this numbers no good
so 344 is not divisible by six the rule for the digit 9 is the same as the rule
for 3 except the sum of the digits must be divisible by 9 not 3 let's look at
some examples we have 657 6 plus 5 plus 7 is 18 which is the same as 2 times 9
so this one works let's look at another one
1989 that's a big number and it adds up to 27 which is the same
as 3 times 9 so both of these numbers we know are divisible by 9 the divisibility
rule the digit 12 is a lot like the rule for 6 except it relies on the rules for
3 & 4 this means that the digits in the
dividend have to add up to a multiple of 3 and the last two digits have to be a
multiple of 4 this is pretty confusing so let's do some examples first we have
216 2 plus 1 plus 6 is 9
which is divisible by three and the last two digits are 16 and 16 is
a multiple of 4 so we know that 216 is divisible by 12 let's do one more
we have 324 3 plus 2 plus 4 adds up to 9 so again it's divisible by 3
and the last two digits are 24 which is a multiple of 4 and because this we know
that 324 is divisible by 12 thank you so much for listening
you can practice divisibility rules with our games which can help you do big math
easier and faster so until next time always be clever