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Number Trail Grade 4 / Week 12 / Tuesday
2/6
Week 12 · Angles, lines and symmetry

Tuesday

Measure and add angles
// Measure, add and sort, then a big review
⏱ about 15 min

Tuesday: Measure and add angles

Ferris the Fox finds a curved tool in Hazel's pencil case. It looks like half a circle.

"That is a protractor," says Bennie the Bear. "It measures angles in degrees."

Ferris folds the corner of his map. The fold splits the square corner into two angles.

He measures them with the protractor. One is 30 degrees, and the other is 60 degrees.

"Thirty and sixty make ninety," says Ferris. "That is the whole square corner!"

"Exactly," says Bennie. "When we split an angle, the parts add up to the whole."

Learn it: measure, then add

A protractor is marked from 0 to 180 degrees.

Put its center on the vertex. Line up 0 with one ray. Read where the other ray crosses.

To sketch an angle, draw one ray, mark the degrees, and draw the second ray.

Two angles side by side, 30 degrees and 60 degrees

Angles add. 30 + 60 = 90, so the whole angle is a right angle.

If we know the whole and one part, we subtract to find the other part.

A right angle split into 50 degrees and an unknown part

The whole is 90 degrees. 50 + ? = 90, so the unknown part is 40 degrees.

ADD THE ANGLES
  • Read the question.
  • Tap your answer.
Two angles side by side, marked 30° and 60°30 + 60 = ?
Two angles side by side, marked 45° and 45°45 + 45 = ?
Two angles side by side, marked 70° and 50°70 + 50 = ?
Two angles side by side, marked 100° and 35°100 + 35 = ?
FIND THE MISSING ANGLE
  • Read the question.
  • Tap your answer.
Two angles side by side, marked 50° and ?50 + ? = 90
Two angles side by side, marked 110° and ?110 + ? = 180
Two angles side by side, marked ? and 25°? + 25 = 90
Two angles make a straight angle. One is 135 degrees. How many degrees is the other?
TOOLS AND SKETCHES
  • Read the question.
  • Tap your answer.
Which tool measures angles?
Ferris sketches a 90 degree angle. What kind of angle is it?
An angle opens a little more than a right angle. Which could be its measure?
MEASURE WITH A PROTRACTOR
  • Think about how Ferris measured the angle.
  • Tap the steps in order.
1First
2Next
3Then
4Last
SentenceTrue or false?
30 + 60 = 90?
110 + 70 = 180?
50 + 45 = 90?
A protractor measures angles in degrees.?
WHY THIS EXERCISE50 + 45 is 95, not 90. The parts must add up to the whole.
Try it
Take a square piece of paper.
Fold it corner to corner to make a triangle.
The fold splits a right angle into 2 equal angles.
Each one is 90 ÷ 2 = 45 degrees.
Draw a right angle. Draw a ray inside it to split it into two angles.

Wonderful! Tomorrow we look at lines and sort shapes.

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