Community organizer: Before last year's community cleanup, only 77 of the local residents signed up to participate, but then well over 100 actually participated.
Conclusion
We can be confident that this year's cleanup will be a success.
Evidence
Before last year's community cleanup, only 77 of the local residents signed up to participate.
Well over 100 actually participated.
This year, 85 residents have signed up to participate.
Our community cleanup will be a success if we have at least 100 participants.
Evaluate
This argument makes a very "confident" prediction about this year's cleanup: it will be a success. That seems to be based on the conditional "if 100+ → success." But do we have enough information to actually trigger that conditional? No way. We only have 85 people signed up. Just because more people showed up than signed up last year doesn't mean that will happen again this year.
Goal
A correct answer might describe this as a type of sampling error: basing a prediction on too small of a sample. It also might point out what we sometimes call a "predictive flaw": predicting the future based on what happened in the past or what's happening in the present. Beware of answers that sound relevant but describe things that don't actually happen in the argument. Also beware of answers that describe other famous flaws which do not occur in this argument.