What is the binary sum of 1 and 1?

• A. 0
• B. 10
• C. 11
• D. 100

Answer: (B)

Binary addition uses base 2, so each digit is 0 or 1. When you add 1 and 1 in the same position, you can’t write 2 in that spot. Instead you write 0 there and carry 1 to the next position. That carried 1 becomes the next digit, giving the result as 10 in binary. In other words, this is the binary way to represent the quantity two. The other strings represent different values: a 0 would come from no carry, 11 represents three, and 100 represents four, none of which match the sum of 1 and 1.