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The second question:

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The third question:

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This part of the extended materials mainly examines the knowledge points of multiples:

An integer can be divisible by another integer, which is a multiple of another integer. For example, 15 can be divisible by 3 or 5, so 15 is a multiple of 3 and 5.

The quotient obtained by dividing one number by another. For example, a÷b=c, that is, A is a multiple of B, for example, A÷B=C, it can be said that A is C times that of B.

A number has countless multiples, which means that the set of multiples of a number is infinite. Note: you can't call a number a multiple alone, you can only say who is a multiple of who.

If one digit of an integer is truncated, subtract twice this digit from the rest. If the difference is a multiple of 7, the original number can be divisible by 7. If the difference is too big or it is not easy to see whether it is a multiple of 7 in mental arithmetic, the above-mentioned "truncation, multiplication, subtraction and difference test" process should be carried out until a clear judgment can be made.

For example, the process of judging whether 133 is a multiple of 7 is as follows: 13-3×2=7, so 133 is a multiple of 7; For another example, the process of judging whether 6 139 is a multiple of 7 is as follows: 6 13-9×2=595, 59-5×2=49, so 6 139 is a multiple of 7, and so on.