They say in 100 years there are 24 leap years, if every fourth year is a leap year, should not it be 25?
The rule is slightly more complex.
Every century is not a leap year, except multiples of 400.
So 2000 is a leap year, but 2100, 2200, and 2300 are not leap years.
In 400 years we would get 100 leap years according to your rule, but 3 of them will not be a leap year, leaving only 97 leap years.
This means that in 100 years, there are actually 97/4=24.25 leap years.
The exceptions being made BECAUSE the year is NOT exactly 365.25 days. By the time every century rolls around, we will have come very close to having had an extra day because of all the leap days, which is why that year is NOT a leap year.