The knowledge points of the third grade elementary school mathematics volume II are classified as follows:

1, commonly used time units are: (hour, minute, second), (year, month, day).

2. 1 year = 12 months 1 day = 24 hours 1 hour = 60 minutes 1 minute = 60 seconds 1 week = 7 days.

3. There are 12 months in a year, including 7 big months, with 3 1 day per month; Abortion lasts for 4 months, with 30 days each month; Sometimes February has 28 days, and sometimes it has 29 days.

There are two ways to judge a flat leap year: the first way is to look at February: there are 28 days in a flat year and 29 days in a leap year. The second method is to divide the year by 4 (integer 100 divided by 400), and the remainder is the average year and the remainder is the leap year.

There is a leap year every three normal years, that is, a leap year every four years. Only leap years have February 29th.

6. The average year is 365 days (365,438+0× 7+30× 4+28 = 365), and the leap year is 52 weeks, 65,438+0 days and 366 days (365,438+0× 7+30× 4+29 = 366).

7, 135780 wax, 3 1 day is not bad, 469 winter 30 days, only February 28, every leap day in four years, it must be added to February.