Remember that if a number is divisible by 15, it must be divisible by the factors of 15, 5 and 3. Also remember that if the sum of the digits of a number is divisible by 3, the number is divisible by 3. So [tex]1+2+3+5+5+8=24[/tex], so all of the six digit numbers are divisible by 3. Additionally, for a number to divisible by 5, it's last digit must be divisible by 5. The probability of this occurring is [tex]2/6=1/3[/tex]
