The first problem that I see is that you haven't provided any HTML code to help us troubleshoot your problem.
So, I've created some temporary HTML code:
<div>Num 1: <span id="num1"></span></div>
<div>Num 2: <span id="num2"></span></div>
<p><input id="txtbox" /></p>
<div>Total: <span id="total"></span></div>
<div>Ans: <span id="ans"></span></div>
<div>Counternumber: <span id="counternumber"></span></div>
I presume that focusIt should be setFocus?
I also notice that some of the variables start with a dollar sign. That's very distracting, because normally that is only done to indicate that the variable contains a jQuery-specific object instead.
With the answer, you are assigning to sumtotal only the result of the current answer. I suspect that you want to instead add the current answer to the existing sumtotal, right?