Divisibilty
If a number is an even number then it can be divided by 2.
e.g. 48 ends with an even digit. It can be divided by 2.
Therefore '2' is one of its factors and so is its partner 24, because 2 x 24 = 48
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If a number ends with a '5' or a '0', then it can be divided by '5'.
e.g. 45 ends with '5'. It can be divided by 5
Therefore '5' is one of its factors and so is its partner 9, because 5 x 9 = 45
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If a the digital root of a number can be divided by 3, then the whole number can be divided by 3
e.g. a) 72 = 7+2 = 9 which can be divided by 3
Therefore 3 is a factor of 72 and its partner is 24 because 24 x 3 = 72
b) 2346 =2 + 3 + 4 + 6 = 15 = 1 + 5 = 6.
Therefore 2346 can be divided by 3.