I think that's a great idea! Other "modes" could really expand it to a full mobile game. Just spitballin':
- Start with addition, then add subtraction, then multiplication.
- Then get really crazy and start changing it up for each input round: addition, multi, sub, sub, add, multi, etc.
- If you really want to challenge ppl, throw in fractions! (;;;*_*)
- Not sure how you'd make it extremely obvious what operation to perform. . .