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Fix apophenia error slowing student progress #1650

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Apr 23, 2020
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Fix apophenia error slowing student progress #1650

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5ee8930
Fix apophenia error slowing student progress
workingjubilee Apr 22, 2020
692ca18
Fix premature doubling in 1st example for Luhn
workingjubilee Apr 23, 2020
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8 changes: 4 additions & 4 deletions exercises/luhn/description.md
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Expand Up @@ -17,27 +17,27 @@ are disallowed.
## Example 1: valid credit card number

```text
4539 1488 0343 6467
4539 3195 0343 6467
```

The first step of the Luhn algorithm is to double every second digit,
starting from the right. We will be doubling

```text
4_3_ 1_8_ 0_4_ 6_6_
4_3_ 3_9_ 0_4_ 6_6_
```

If doubling the number results in a number greater than 9 then subtract 9
from the product. The results of our doubling:

```text
8569 2478 0383 3437
8569 6195 0383 3437
```

Then sum all of the digits:

```text
8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80
8+5+6+9+6+1+9+5+0+3+8+3+3+4+3+7 = 80
```

If the sum is evenly divisible by 10, then the number is valid. This number is valid!
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