What this skill covers
Geometry questions on the ACT are generally direct formula applications for area, perimeter, volume, and right triangles. Statistics questions test whether you can correctly compute or read off a mean, median, or simple probability.
For probability questions phrased as "one is selected at random," the answer is always (number of favorable outcomes) ÷ (total number of outcomes) — write out both numbers explicitly before dividing.
Worked examples
Example 1
A rectangle has a length of 9 and a width of 4. What is its perimeter?
A. 26
B. 36
C. 13
D. 18
Why: Perimeter = 2(length + width) = 2(9 + 4) = 26 — a common wrong answer, 36, comes from computing area instead.
Example 2
A bag contains 4 red, 3 blue, and 3 green marbles. What is the probability of selecting a red marble at random?
A. 4/10
B. 4/3
C. 3/10
D. 1/4
Why: There are 10 marbles total and 4 are red, so the probability is 4/10 — always divide by the total count, not by one of the other colors.
How to practice this on TSI Practice Prep
Open ACT Practice to answer original ACT questions on aCT Geometry and Statistics, get an explanation for every choice, and see this skill tracked separately in your progress and mistake review.
Practice score estimates are learning indicators, not official scores or admission guarantees.
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