Worked Example 1
Inside a Right Angle
A right angle is split into two angles. One is 38°. Write an equation and find the other angle.
- 1A right angle is 90°: 38 + x = 90
- 290 − 38 = 52
Answer: x = 52°
Florida Grade 4 Math · Geometric Reasoning
MA.4.GR.1.3: Finding Unknown Angle Measures
What this Grade 4 benchmark means, worked examples, common mistakes, and a free printable worksheet.
Created by a Florida mom · Published by Tropical Learning LLC
What Is Benchmark MA.4.GR.1.3?
Students solve problems with unknown angle measures, and write an equation with a letter for the unknown.
Because angle measures are additive, if an angle is split into parts, the parts add up to the whole. For example, if a 60° angle is split into two angles and one is 25°, then 25 + x = 60, so x = 35.
Official benchmarkSolve real-world and mathematical problems involving unknown whole-number angle measures. Write an equation to represent the unknown.
On the FAST test: part of the Grade 4 reporting category Geometric Reasoning, Measurement, and Data Analysis and Probability, which is about 31–37% of the test.
Worked Examples
Worked Example 2
On a Straight Line
Two angles together make a straight angle. One measures 115°. Find the other.
- 1A straight angle is 180°: 115 + a = 180
- 2180 − 115 = 65
Answer: a = 65°
Common Mistakes to Watch For
Adding instead of subtracting
Wrong:38 + x = 90, so x = 90 + 38 = 128
The parts add to 90, so subtract: x = 90 − 38 = 52°.
Using the wrong total
Wrong:Two angles on a straight line add to 90°.
A straight angle is 180°. A right angle is 90°.
Helpful Math Tip
Write the equation first (part + part = whole), then solve. It keeps the thinking organized.
Related Grade 4 Skills
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Start Practicing FreeIndependent Educational Platform. FastChomp is published by Tropical Learning LLC and is not affiliated with, sponsored by, or endorsed by the Florida Department of Education. FAST and Star assessment names are referenced for informational purposes only. FastChomp practice questions are original educational materials, not official Florida FAST assessment questions.