How to calculate the third grade mathematics in primary school? Which year is the average year and which year is the run year?

1, the annual scale is not a whole hundred years. Divide the chronology by 4, and the year with the remainder of 0 is a leap year.

The year in which the remainder is not 0 is the average year.

For example: 2008, 2008÷4=502, and the remainder is 0, so 2008 is a leap year;

In 2009, 2009 ÷ 4 = 502... 1, and the remainder is 1 (the remainder is not 0), so 2008 is a normal year;

2010,2010 ÷ 4 = 502 ... 2, and the remainder is 2 (the remainder is not 0), so 2008 is a normal year;

1986,1986 ÷ 4 = 496 ... 2, and the remainder is 2 (the remainder is not 0), so 2008 is a normal year;

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2. The annual scale is a whole hundred years. Divide the chronology by 400, and the year with the remainder of 0 is a leap year.

The year in which the remainder is not 0 is the average year.

For example: 2000,2000 ÷ 400 = 5, and the remainder is 0, then 2000 is a leap year;

2 100, 2 100 ÷ 400 = 5 ...100, and the remainder is100 (the remainder is not 0), so 2100 is a normal year;

1900,1900 ÷ 400 = 4 ... 300, and the remainder is 300 (the remainder is not 0), so1900 is a normal year;

1800,1800 ÷ 400 = 4 ... 200, and the remainder is 200 (the remainder is not 0), so1800 is a normal year;

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Formula: One leap every three years and one leap every hundred years.