Highscore and time limit would make it a bit more appealing though.
Funny thing is that I created something similar on my Atari ST ages ago in GFA basic. A certain amount of calculations (I think 10) needed to be finalized asap. The high score was just the fastest time needed to finalize the calculations and every wrong answer costed a huge amount of seconds.
Too bad I sold the ST and threw away the disks with this program. It wasn't a complicated program, but it was by far my best programming attempt..