Grade 6 › U03 Decimal Operations

Grade 6 › U03 Decimal Operations › L3
NUMBER · GRADE 6 · ALBERTAOUTCOME AB-MAT6-N4

L3 · Multiplying decimals

Learning goal

“I can multiply a decimal by a whole number and by another decimal by thinking in tenths and hundredths, and I can use an estimate on a number line to place the decimal point - and to prove my answer is the right size.”

Product — the answer to a multiplication. 2.4 x 3 has product 7.2.
Place value — the value of a digit because of where it sits: ones, tenths, hundredths. 2.4 is 24 tenths; 1.25 is 125 hundredths.
Estimate — a quick, rounded calculation that predicts the size of the answer before you compute it, so you can check the decimal point afterwards.
Hundredths grid — a 10 x 10 square worth 1 whole. Each column is 1 tenth (0.1); each small square is 1 hundredth (0.01). Used to see a decimal x decimal product.
Worked example

Multiply 2.4 x 3. Step 1: Estimate first. 2.4 sits between 2 and 3 on the number line, so 2.4 x 3 sits between 2 x 3 = 6 and 3 x 3 = 9. The product must land between 6 and 9. Step 2: Rename by place value. 2.4 is 24 tenths (place-value chart: 2 ones = 20 tenths, plus 4 tenths). Step 3: Multiply the count. 24 tenths x 3 = 72 tenths. Step 4: Rename back. 72 tenths = 7 ones and 2 tenths = 7.2. Check against the estimate: 7.2 is between 6 and 9. The digits were 72, but the answer is 7.2 - the place value, not the digits alone, sets the point.

Check yourself — explain it

Why is 2.4 x 3 equal to 7.2 and not 72?

Paired problem — example still visible

Multiply 1.6 x 4. -> 16 tenths x 4 = 64 tenths = 6.4

Faded completion — last step is yours

"0.9 x 5: estimate is about 1 x 5 = 5. 9 tenths x 5 = 45 tenths, so 0.9 x 5 = ___" -> 4.5

Ready to practise?

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

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