Grade 4 › G4U09 Area & Angles

Grade 4 › G4U09 Area & Angles › L3
GRADE 4 · ALBERTAOUTCOME AB-G4-4M1

L3 · Estimating Area: A Square-Centimetre Referent; Rearranging Keeps the Area

Learning goal

“I can estimate an area by picturing how many square centimetres (about a fingernail each) fit on it - and I know that cutting a shape into pieces and rearranging them does NOT change its area.”

Referent — a familiar object you picture to stand for a unit. For 1 cm², the referent is about the size of a fingernail.
Estimate — a sensible close answer found without exact measuring, on purpose.
Rearrange — to cut a shape into pieces and put the same pieces back together in a new arrangement.
Partial unit — a part of a unit square (like a half square) that a curved or slanted edge covers; partial units can be combined to make whole units.
Worked example

Estimate the area of a birthday card without a ruler or grid. Step 1: Picture the referent: 1 cm² is about a fingernail. Step 2: Picture fingernail squares along the card's width: about 10 fit across. Down its length: about 15 fit. Step 3: Estimate: about 10 x 15 = 150 cm². (An estimate is allowed to be close, not exact - that's its job.) Say it plainly: estimating area = picturing the referent unit tiled over the surface, counting how many fit across and down, then multiplying like a rectangle.

Check yourself — explain it

An estimate of area is useful because...

Paired problem — example still visible

A book cover fits about 12 fingernail squares across and about 18 down. Estimate its area. -> about 216 cm² (12 x 18 = 216; accept 180-250)

Faded completion — last step is yours

"A mat fits about 8 cm squares across and 5 down: estimate = 8 x ___ = about ___ cm²" -> 5; 40 cm²

Ready to practise?

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

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