Credit card numbers are not assigned at random. Who new? By looking at a credit card number and doing some simple math (addition and multiplication), you can
verify if a credit card number is real or not. So,
business owners, before you accept a random credit card number as payment and find out you were bamboozled, ask the customer to wait a minute and give this a whirl.
Budget Planner Software - Mint.com
When I did this for myself, I thought the highlighted step (see image below) was kind of confusing. I made some arrows to show you how they added the non-doubled numbers to the doubled ones for clarification.
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| Follow the arrows |
