Got it, I thought that is for hints.
I apologize for that.

Hey Guys, I found that so many people didn't read it carefully.

• number of inhabitants is an integer.
  
• It means you should NOT return FLOAT
  
• So you can use Math.floor to make the return to be INTEGER.
  
• You won't fail to nbYear(1000, 2.0, 50, 1214) again.