Step one

Take the credit card number below and double every other digit from the left (marked in raised numbers below). (I got this number off an ad on the internet).

5424 1801 2345 6789

5x2=10; 2x2=4; 1x2=2; 0x2=0; 2x2=4; 4x2=8; 6x2=12; 8x2=16.

(You should come up with the following sequence of numbers: 10, 4, 2, 0, 4, 8, 12, and 16.)

Step two

Add the new numbers (10, 4, 2, 0, 4, 8, 12, and 16) to the numbers you didn't double (4, 4, 8, 1, 3, 5, 7 and 9) in the above card number.

All double digits (like 10, 12 and 16) should be added as a sum of their digits. An example would be: 10 becomes 1+0; 12 becomes 1+2 and 16 becomes 1+6).

1+0+4+4+4 + 1+8+0+1 + 4+3+8+5 + 1+2+7+1+6+9 = 69

Step three

If the final sum is divisible by 10, then the credit card number is valid. If it cannot be divided by 10, the number is invalid or fake.

69 10 = 6.9

As you can see, the number I got off the ad is a fake or invalid number. Grab a credit card out of your wallet and try this simple and fun test.

Source

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