BODMAS

What? Shush - all will be revealed in due course.  You know I like these little maths puzzles, so here's one for you -

9 - 3 ÷ 1/3 + 1 = ?

If you simply work from left to right, you have nine minus three, which is six; six divided by one-third (you may remember from school that this is the same as six multiplied by three) which is eighteen, and then plus one gives an answer of nineteen. But were you taught BODMAS, or something similar?  The point is that you don't just work from left to right, but some calculations take precedence over others.  The order - as I was taught it, is -
          B(rackets)
          O(f)
          D(ivision)
          M(ultiplication)
          A(ddition)
          S(ubtraction)
- specifically, multiplication and division must be done before addition and subtraction, So the first thing you must do is deal with the "three divided by a third" bit, and three divided by a third is the same as three multiplied by three, which is nine. So the sum now becomes nine minus nine plus one, which is of course one.  So the answer is one.