Solution:
Calculation:
The number which divisible by 3 =3Last term−First term+1=3999−102+1=300
The number which divisible by 5 =5Last term−First term+1=5995−100+1=180
The number which divisible by 15 =15Last term−First term+1=15990−105+1=60
So, the total number of three-digit numbers divisible by 3 or 5 = 300 + 180 - 60 = 420.
∴∴ The correct answer is 420.