Grade 4 › G4U09 Area & Angles

Grade 4 › G4U09 Area & Angles › L6
GRADE 4 · ALBERTAOUTCOME AB-G4-4M2

L6 · Angle Benchmarks: 45°, 90°, 180°, 270°, 360° as Fractions of a Circle

Learning goal

“I can name the benchmark angles - 45°, 90°, 180°, 270°, 360° - as fractions of a full circle, and I can estimate an angle's measure by comparing it with the benchmarks.”

Benchmark — a known angle you compare other angles to (45°, 90°, 180°, 270°, 360°).
Quarter turn — a turn of 90°, one quarter (1/4) of a full circle.
Half turn — a turn of 180°, one half (1/2) of a full circle.
Full turn — a turn of 360°, the whole circle (4/4).
Worked example

Build the benchmark set from the full circle. Step 1: Full turn = 360° = the whole circle = 4/4. Step 2: Half turn = 360 / 2 = 180° = 1/2 of the circle. Quarter turn = 360 / 4 = 90° = 1/4. Three-quarter turn = 90 + 90 + 90 = 270° = 3/4. Step 3: Half of a quarter turn = 90 / 2 = 45° = 1/8 of the circle. Say it plainly: the benchmarks are just the friendly fractions of the circle - 1/8, 1/4, 1/2, 3/4, and the whole - wearing degree labels.

Check yourself — explain it

270° is 3/4 of a circle because...

Paired problem — example still visible

What fraction of a full circle is 180°, and what turn is it? -> 1/2; a half turn

Faded completion — last step is yours

"A three-quarter turn: 90 + 90 + 90 = ___°, which is ___ of a full circle" -> 270; 3/4

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

Start practice →Take the unit quiz