Answer:
Explanation:
It is more frequently used to find primes, oddly enough.
Write down the first 25 numbers.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Start with 2. Use your eraser and jump to 4. Erase it because 2 will divide into 4. Leave 5 alone. 2 won't go into 5. But it will into 6. Erase six. Leave 7. Go to 8 and erase it. Leave 9 erase 10. Leave 11. Erase 12. Leave 13. Erase 14. Erase 16,18,20,22,24,26,28,30 all for the same reason. Two will divide into each of them.
Start with 3 can't do anything. 3 stays 6 is gone erase 9 . 12 is gone. Erase 15. 18 is already gone. Erase 21, 24 is gone. Erase 27. 30 is gone already.
Do the same with 5, 7, 11, 13,17,19,23 (you do run out of numbers to erase)
The sieve leaves behind the primes.
Anything you have erased is a composite.