# How Computers Add Numbers

**How Computers Add Numbers**

Computers turn every number into binary. The numbers that we use are expressed in base 10. Every 10 1s equals 1 ten, every 10 tens equals 1 hundred, and so on. In binary, you go up a unit every 2 numbers. So 2 ones equals 1 two, 2 twos equal 1 4, and so on. For example, the number 9 would be 1001 in binary: 1 one, 0 twos, 0 fours, and 1 eight. 1 + 8 =9. Computers do this because it is easier to design circuits that only have values of 1 or 0 than circuits with 10 separate values each.

Computers have basic mathematical operations like addition and subtraction programmed into them. Adding in binary is extremely simple. If you have 2 numbers with a 1 value, you store a 0 and move carry 1. Otherwise, you record the bigger of the two numbers in that slot. For example, if you are adding 5 + 4, you get: 0101 + 0100. In the first slot, you have a 1 + 0, so you store the bigger number, 1. In the second slot, you have two 0s, so you store 0 (since both numbers are the same. In the third slot you have two 1s, so you store a 0 and carry a 1. You end up with the number 1001, or 9.

See how computer add numbers.