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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 digital knowledge points:

The position of each number in a number. The number of digits in the integer part starts from the right, and every four digits are one level, and each level includes one digit, ten digits, hundred digits and thousand digits, indicating how many ones there are; Tens of thousands include tens of thousands, hundreds of thousands, millions and tens of millions, indicating how many tens of thousands there are; Billions include hundreds of millions, billions, tens of billions and hundreds of billions, indicating that billions ... Decimal numbers are deciles, percentiles and thousandths from left to right ... indicating tenths, percentiles and thousandths. ...

The number of digits of a natural number is called the number of digits. For example, the number 9 contains only one number, so 9 is a number; Five digits 12345 contains five digits: one, ten, hundred, thousand and ten thousand.

The decimal counting method is characterized by "full 10 into one". In other words, every 10 unit forms a higher unit adjacent to it. That is, 10 is called "ten", 10 is called "hundred", 10 is called "thousand" and 10 is called "ten thousand".

One (a), ten, hundred, thousand, ten thousand, one hundred thousand, one million (trillion), ten million, one billion, ten billion, one hundred billion ... are all units of counting.