SME
Grade 4 Math · Measurement & Data
Angles and angle measurement
Use this for “Angles of 35° and 55° share a ray. What is the whole angle?” or a part from the whole.
Diagram
35° and 55° make 90°: a right angle.
This is an example. Type your own values to start a new problem.
First angle
°
+
Second angle
°
=
Whole angle
°
Formulas
35 + 55 = 90
First angle + second angle = whole angle
Assumptions
•
A full turn is 360 degrees. One degree is 1/360 of a turn.
•
A right angle is 90°: a quarter turn. A straight angle is 180°: a half turn.
•
Two angles that share a vertex and a ray add up: the whole angle is their sum, up to a straight angle.
•
Give the whole angle and one part to find the other part: the parts subtract.
•
Drag the middle ray, or use the sliders, to change the angles.
Step-by-step
WE KNOW
First angle: 35°
Second angle: 55°
FIND
whole angle
Step 1 · Find whole angle
35 + 55 = ?
First angle + second angle = whole angle
Add the two angles: they share a ray, so together they make the whole angle.
1
3
5
+
5
5
9
0
Whole angle = 90° (a right angle)
Check
Put the numbers back in. Both sides should match.
35 + 55 = 90 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
Refresh
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More problem types
Measure angles with a protractor
Use this for “What is the measure of the angle?” on a protractor, either scale.
Measure angles: neither ray on zero
Use this for “One ray points to 45 and the other to 135. What is the angle?”
Understand angles as parts of a turn
Use this for “a quarter turn is how many degrees?” or “how many 20° angles make a full turn?”