ACT · Elementary Algebra · Substitution and evaluation
Question act-q-00318
Medium Multiple choice No calculator
The question
If f(x) = 5x² − 2, what is the value of f(3)?
- -43
- 43
- 13
- 44
Show answer & worked solution
Answer: 43
Worked solution. Substitute x = 3: f(3) = 5 × (3)² − 2 = 5 × 9 − 2 = 45 − 2 = 43.
Why each wrong choice is wrong. Forgetting to square the input is the dominant error — the linear-substitution distractor catches it.
Test-day tactic. Substitute with parentheses around the input. (3)² always equals 9, regardless of the sign of 3.
About this question type
A value or set of values is given for the variables; substitute and compute. The arithmetic can be tricky when negatives or fractions are involved.
You will see a question shaped like this one on roughly every other official ACT form, typically at a moderate position in the section — solidly within the range that separates a 600-band student from a 700-band student. Treat any miss in this subtopic as a signal to drill the subtopic page before you do another full practice test.