I have to go with LH on this one....it is great to have tools like a calculator but if you don't know how to do it without and understand the why you haven't learned to do the task. What happens if you need to do some calculations and don't have a calculator available? If you always depend on a calculator how do you know if a number looks "off?" You will have to accept what someone else tells you the number should be.

I am not a math whiz but I force myself to do manual calculations periodically just to make sure I still can!