For simple question like that, you shouldn't even need a piece of paper to figure out the answer. It is definitely alright to say 'standby' in the commercial flying world. If you need, you can even request a holding pattern to figure out the answer. =) What ever you need to do to do what's need to be done. I've never seen anyone doing that in real life though. What i wanted to say is, when you are flying, try to come up with a simple system that you can work with so you don't need to pull out a piece of paper everytime.
For the numerical test, no body can answer all the question. If you can, you are a genius in math.