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.
Below are the available bulk discount rates for each individual item when you purchase a certain amount. 1  Buy 10 - 99 and pay only $5.00 each. 2  Buy 100 - 499 and pay only $4.00 each. 3  Buy 500 - 999 and pay only $2.25 each. 4  Buy 1000 or above and pay only $1.50 each.