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SAT · Math · Geometry and Trigonometry

Lines, Angles, and Triangles on the Digital SAT: How to Answer These Questions

Whether you can use angle relationships, triangle properties, congruence and similarity.

By Hourly Prep Editorial TeamReviewed October 1, 2026

How to answer it

  1. Mark every angle you know on the figure.
  2. Use 180° for triangles and straight lines.
  3. Use equal angles from parallel lines or similar triangles to fill in the rest.

Worked example

An original question in the SAT format, already answered.

SAT MathWorked example

Two angles of a triangle measure 48° and 67°.

What is the measure of the third angle?

  1. A55°
  2. B65°
  3. C115°
  4. D135°

Answer: B. 180 − (48 + 67) = 180 − 115 = 65. Choice C is the sum of the two given angles.

The most common trap

Stopping at the sum of the known angles. Subtract it from 180.

Practice it

Hourly Prep’s daily sets mix lines, angles, and triangles with the rest of SAT Math, and send more of it your way when it’s a weak spot. See how the SAT prep plan works, or browse the other SAT skill guides.

Primary sources

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Practice lines, angles, and triangles in 15 minutes a day.

Short SAT sets on the test-day screen, with an explanation for every question.

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