To explain the leap year, let's use the example that if the sun is behind by 0.25 days (6 hours), then, in four years, the sun is behind by 0.25 days x 4 = 1 day (24 hours). We add a day, 2/29, to the fourth year so that the sun will catch up with our calendar perfectly. But the sun is only behind by 0.2422 days. In 4 years, the sun will be behind by 0.2422 days x 4 = 0.9688 days. We add one day on 2/29, which is a little too much. 1 day minus 0.9688 days = 0.0312 days. Then, in 100 years, we add too much by 0.0312 days x 25 (25 leap years in 100 years) = 0.78 days. Therefore, there is no leap year in every hundred years. Then again, we have to add a leap day (2/29) every 400 years. Use a table to show whether a year from 2000 to 2100 is a leap year or not. Use four columns in your table so it will not be too long