Credit card numbers follow certain patterns. A credit card must have between 13 and 16 digits. It must start with: â¢ 4 for Visa cards. â¢ 5 for Master cards. â¢ 37 for American Express cards. In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine if a card number is entered correctly or if a credit card is scanned correctly by a scanner.
The phrases used for discounted items include,  off, Save 50%, and Get a 20% discount.. Procedure: 1  To calculate the discount, multiply the rate by the original price. 2  To calculate the sale price, subtract the discount from original price.
Interest rates are usually expressed on an annualized basis. If someone lends you $100 and you agree to repay him $110 in six months, the six-month rate of interest is 10%. But 10% every six months is 20% per year. That is, the annualized rate of interest is 20%.o, you receive only $90 in cash today, but the day the loan is due you'd only hand over $100 (because you already paid the $10 interest up front). In essence, the lender bought your $100 bond at a discountit only cost him $90 today. You can read more about the details in a book on interest rates.