Riya's bus ticket number got smudged (?). She remembers the number was divisible by 8. How many different digits could be under the smudge?

For 8, only the last three digits matter: ?24 must be divisible by 8. $024,224,424,624,824$ are (e.g. $224=8\times 28$); $124,324,524,724,924$ are not. So 5 digits: 0, 2, 4, 6, 8. (10 comes from checking only the last two digits, which is the rule for 4.)