How to work out numbers involving leap year.

To work out numbers involving leap years, you need to understand the rules for determining if a year is a leap year. Here are the rules:

1. A year is a leap year if it is divisible by 4.
2. However, if the year is divisible by 100, it is not a leap year, unless it is also divisible by 400.

Based on these rules, you can determine if a given year is a leap year or not. For example, 2020 is a leap year because it is divisible by 4. However, 1900 is not a leap year because even though it is divisible by 4, it is also divisible by 100 but not by 400.

Once you have determined if a year is a leap year, you can work out numbers involving leap years by taking into account the extra day in February (29 days instead of 28). This can affect calculations such as determining the number of days between two dates, calculating interest rates, or any other numerical calculations that involve dates and time periods.

It is important to remember to consider leap years when working with dates and time periods to ensure accurate calculations.

1. Determining if a Year is a Leap Year:

- A year is a leap year if it is divisible by 400 or it is divisible by 4 but not by 100.

2. Calculating Days in a Year:

- A typical year has 365 days.
- A leap year has 366 days, with the extra day added to February as February 29th.

3. Calculating Days in a Leap Year:

- Days in February: 29
- Days in other months: Same as in a typical year (31 for January, March, May, July, August, October, December; 30 for April, June, September, November)

4. Calculating Days in a Time Period:

- Total days in a typical year: 365 days
- Total days in a leap year: 366 days
- Days in a specific number of years:

```
Total days = (Number of years) x (Days per year)
```

- Days in a specific number of years, including leap years:

```
Total days = (Number of years excluding leap years) x (Days per typical year) + (Number of leap years) x (Days per leap year)
```

Example:

- Calculate the total days from January 1, 1990, to December 31, 2006.

Solution:

- There are 17 years in this period (from 1990 to 2006).
- 4 of these years are leap years (1992, 1996, 2000, 2004).
- Total days = (13 x 365) + (4 x 366)
- Total days = 4745 + 1464
- Total days = 6209