Number is for things you can count. Amount is for things you measure. A number of questions. An amount of time. The ACT pairs this with less and fewer, which is already covered in comparison words.
Count or measure
Questions, students, misses, and points take number. You can count them one by one. Time, work, practice, and energy take amount. You measure those. The number of blanks is right. The amount of blanks is the trap.
Fewer goes with the countable noun. Less goes with the mass noun. Fewer misses, less time. Do not rebuild that rule here. Use the comparison-words page when the choice is less versus fewer.
Agreement follows the noun
The number of students is singular. A number of students are plural. The verb has to match. That pattern is in subject-verb agreement. Diction overall is in word choice, and the grammar map is in ACT grammar rules.
The bottom line
If you can count the units, say number. If you can only measure the stuff, say amount.
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.