How to answer it
- Write a variable for the unknown dimension.
- Use the given relationship to build an equation.
- Solve, then answer the exact question asked.
Worked example
An original question in the ACT format, already answered.
ACT MathWorked example
A rectangle’s length is 3 times its width, and its perimeter is 48 inches.
What is the area of the rectangle, in square inches?
- A72
- B96
- C108
- D144
Answer: C. 2(w + 3w) = 48, so 8w = 48 and w = 6. The length is 18, and the area is 6 × 18 = 108.
The most common trap
Stopping once you know the width. The question asks for the area.
Practice it
Hourly Prep’s daily sets mix geometry with the rest of ACT Math, and send more of it your way when it’s a weak spot. See how the ACT prep plan works, or browse the other ACT skill guides.