What is one plus three?

Answer 1

The answer is 4 as according to the Addition Theorem. It states that "to add a sum or equation, take the added number and thereby split it into the lowest possible whole number, before adding it up." So 1+3 = 1+(1+2) = 1+ [(1+1)+1] = (1+1) +(1+1) = 2+2=4.

Answer 2

The answer is 4. Simply add the first two numbers together by using basic arithmetic skills. To check your work, a calculator is always a good option.