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Divisibility Tests

Divisibility by 4 Test:

This one works great - about half of the time.

A number is divisible by 4 if the last two digits
are a number that's divisible by 4.


Let me make that clearer:

Look at the last two digits of a number...
 

23,524 Does 4 go into 24? Yep!

So the whole thing is divisible by 4.
 

What about this guy?

Does 4 go into 572? ( Is 572 divisible by 4? ) Does 4 go into 72?
 

Hmm...  I don't know that one off the top of my head... because it's not an answer from our times tables!

These I know:

4, 8, 12, 16, 20, 28, 32, 36, 40, 44 and 48
 

Anything past that I'd either have to check with a calculator or long division...  But, I could do THAT for 572 too!  If it was a really big number, like 7,283,472, just checking the last two numbers would save a lot of time, though.

So, this test is great for numbers that end in 48 or less and for really big numbers.