How can you test to determine whether a number is a factor of another number?

#1 For any EVEN number it will divide by '2'. So '2' is a factor.

e.g. 1,000,004

#2 For any number ending in '5' or '0' it will divide by '5'. So ;5; is a factor.

e.g. 505, or 1050

#3 For any number where the digits sum/add to '9' , then it will divide by '9'. So '9' is a factor. e.g. 153 ( 1 + 5 + 3 = 9)

#4 For any number where the inside digits sum to the total of the outside digits, then '11' is a factor . e.g. 132 (1 + 2 = 3)

#5 The only two numbers you MUST test mechanically are '3' & '7'.