Which sampling method is generally the weakest

 The answer to that question is Random Sampling

We can use our shortcuts to test if 4221462 is divisible or not by a certain number:
All integers are divisible by 1.
This is even, so it is divisible by 2.
The sum of the digits of this number is divisible by 3, so the whole number is divisible by 3.
The last two digits of this number are not divisible by 4, so it is not divisible by 8 either.
This number is not divisible by 5 or 10, because it doesn't end with a 5 or 0.
This number is divisible by 6, because it is divisible by two and three.
This number is divisible by 7.
The sum of the digits of this number is not divisible by 9, so the whole number is not divisible by 9.
We get 1 + 2 + 3 + 6 + 7 = 19.
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Hope this helps!