It's boring at some point. You should make a countdown instead: you have, say, 1 minute to answer as much questions as you can (with an possible skip button).
At first I actually thought that's what the game would be. I was pleasantly surprised that it was more like juggling, by the end when I had 1-2 seconds per problem, I was far more interested. Something about keeping up the "combo" but testing my arithmetic was quite pleasurable.
