There are 1,826 days in 5 yr. In relation to the leap year, there are 1826.25 days in 5 yrs. That is because there are really 365.25 days in a year (making every four years a leap year). So, when you multiply 365.25 by 5, you get 1826.25.
If you know that 
, then you know right away
###
Otherwise, you can derive the same result. Let 
, so that 
. 
is bounded, so we know 
. For these values of 
, we always have 
.
So, recalling the Pythagorean theorem, we find
Then
as expected.
The probability of flipping 1 head when flipping 3 coins is 3/8.
Hope I helped!
