There are 16 digits on a Mastercard...not including the expiry date, of course.
which mastercard starts with 5111
4 lots of 4 digits.
It depends on the credit card. Visa and Mastercard both have 16 digits. American Express has 15.
16 digits
It would depend on the Credit Card type. Visa, Mastercard, and Discover are 16 digits American Express is 15 digits Diners Club is 14 digits
Debit cards, credit cards have 16 digits. Usually a "plain" ATM (without the visa/mastercard logo) has fewer.
On the back of the card, the last 3 digits on the signature bar
Probably not. Some of the digits are probably check digits, calculated from the other digits, based on some formula. This means that if any one of the digits changes, another digits - or other digits - have to change, too.
Credit card ID numbers have three (Discover, Visa, MasterCard) or four (American Express) digits.
A Visa and/or Mastercard will most likely have 16 digits. Most Visa's start with the number '4' and Mastercards with the number '5'. Gas cards, department store cards, debit cards can have anywhere from 7 digits to 16 digits.
Technically zero, as there are no numbers in the word "credit card". Otherwise, Visa, Discover, MasterCard, nearly all major companies have 16 digits. American Express on the other hand, have 15 digits.