During a year that is not a leap year it is April 10. For leap years it is April 9.
The 9th of April was the 100th day of the year 2000.
The 100th day of the year 2012 is April 9th (because of a leap year).
During a year that is not a leap year it is April 10. For leap years it is April 9.
9 April
In regular years, the 100th day of the year is the 10th of April. In leap years, it's the 9th of April.
The 100th day of the year is April 10, on a normal calendar year, April 9 on a leap year.
April 10th is the 100th day of the year.
April
April 10th in a normal year or April 9th if it is a leap year.
The 100 day of the year is either April 10th - or April 9th in a leap year.
It is in April. It is the 10th in a normal year and the 9th in a leap year.
Centenary means the 100th anniversay, which would be the 100th year.