Does $3-4+1$ equal $0$ or $-2$.. or maybe $2$? Does $3 - 4 + 1 = 0$ or $3 - 4 + 1 = -2$?
Makes sense that $(3 - 4) + 1 = 0$ and $3 - (4 + 1) = -2$, but what if there are no parenthesis?
Also, if I have $4$ apples and I add $1$ more apple, then I have $5$ apples, but if I eat $3$ apples, then I have $2$ left.
Any ideas?

If you want to find the answer to 3 - 4 + 1, you have to use PEMDAS. Since there's no parenthesis, exponents, multiplication, or division, we go to the A and S; addition and subtraction. To do this, you do it left to right. You do 3 - 4 first, which is -1, then you add 1 to that, so you get 0. So, there you go. Using simple PEMDAS, we can say that the answer is 0. Remember: If you have a problem with multiple operations, but no parenthesis, use the MDAS rules, which states that in multiplication and division/addition and subtraction, solve left to right. Thus, 3 - 4 + 1 is 0.
