Odd and Even Numbers

Step 1 of 5

Try to pair everything up.

Take a pile of counters and put them in twos. If nothing is left over, the number is even. If one is stranded, it is odd.

Step 2 of 5

Even numbers split in half exactly.

Because they pair up, even numbers can always be shared between two people with nothing left. Odd numbers cannot, without cutting something.

Step 3 of 5

The last digit gives it away instantly.

Any number ending in 0, 2, 4, 6 or 8 is even. Ending in 1, 3, 5, 7 or 9 makes it odd. It works for 6 and for 6,483,712 alike.

Step 4 of 5

They alternate forever.

Count up and you flip between odd and even every single step, with no exceptions anywhere along the number line.

Step 5 of 5

Adding follows neat rules.

Even plus even is even. Odd plus odd is also even — the two lonely ones pair up with each other. Odd plus even is odd.

Computers care a lot about this. Checking whether a number is even is one of the fastest tests a processor can do.