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Math is less than 30 in the first grade.
Between 30 and 40, excluding 30 and 40, so * * has 9 numbers: 3 1, 32, 33, 34, 35, 36, 37, 38, 39.

When counting, count to dozens, and you want to know what the next integer is.

The relationship between counting units "one", "ten" and "hundred" is: 10, one is ten, and 10 is one hundred. The propulsion rate between every two adjacent counting units is 10.

Extended data

Number sequence within 100: from the right, the first digit is one digit, the second digit is ten digits, and the third digit is one hundred digits.

Read and write numbers within 100:

Number sequence within 1 and 100: from the right, the first digit is one digit, the second digit is ten digits, and the third digit is one hundred digits.

2. Both reading and writing are high. When reading, you should read hundreds of miles, dozens of miles, a few digits, and don't read the last 0; When writing numbers, the hundredth digit writes hundreds, the tenth digit writes tens, the first digit writes ones, and the last counting unit is empty, so write a zero there.