Fewer is for things you can count. Less is for amounts you measure. Fewer questions. Less time. This is one comparison-word split, not the whole set in comparison words.
Can you number them?
If you can say one, two, three, use fewer: fewer errors, fewer students, fewer pages. If you cannot, use less: less water, less patience, less homework. Less questions is the usual miss.
Countable versus mass nouns also show up as amount versus number. Quantity words that pair with this split are in much versus many. Diction overall is in word choice.
The bottom line
Countable items: fewer. Uncountable amounts: less.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.