Practice the missing number UPC problems from last time, and do these:
Missing numbers in check routing numbers:
1. Bank routing numbers use a 7-3-9 rule (mod 10). Use the bank routing number rule to check which of these codes could be valid (has a correct check digit):
| 2 1 5 8 7 2 9 4 6 | |
|
| 2 1 1 8 7 2 9 4 6 | |
|
| 2 1 1 8 7 2 0 1 6 | |
2. Find the missing digit in each of these bank routing numbers:
| ? 1 3 7 8 2 4 6 1 |  |
|
| 2 ? 6 9 2 4 4 1 7 | |
|
| 1 3 ? 6 2 7 9 1 5 | |
|
| 4 2 6 ? 6 6 9 1 1 | |
|
| 8 8 1 5 ? 7 1 0 2 | |
|
| 6 4 1 3 8 ? 8 1 3 | |
|
| 4 0 2 2 5 0 ? 6 1 | |
|
| 9 0 1 1 5 8 9 ? 0 | |
|
| 1 3 3 8 6 5 4 4 ? | |
And the question I forgot last time:
3. What are check digits good for? Why do they bother to put check digits on UPC codes and things like that?