Time is continuous.
If it was possible to measure EXACTLY the time it
takes a person (or group of people) to evaluate 27 + 72 (=99), the
time(s) people took could be 2 seconds, 3 seconds, 2.5 seconds, 2.25
seconds, 2.22 seconds, 2.2199999 seconds... In other words, any value is
possible when measuring "exact" time elapsed.
However, people are
limited by the tools they use. There isn't a tool without limits in its
ability to measure time elapsed. For example, is the stopwatch accurate
to 1/100th of a second? 1/1000th of a second? At some point it reaches
its limit. The constraints of the tool being used to measure are going
to, in fact, cause data to be "discrete."
I'm 90% sure you're
teacher is looking for "continuous" as the solution though. So don't
bring up "discrete" unless you feel like you'll be able to confidently
explain the second paragraph above.