Multiplying Decimals
Aligned to 5.NBT.B.7 — Common Core State Standards for Mathematics.
What this lesson teaches
Multiply as if there were no decimal points, then count how many decimal places are in BOTH factors together and place that many in the answer.
Worked examples
Example 1
1.2 × 0.4 → 12 × 4 = 48. One decimal place + one decimal place = two places, so 0.48.
Example 2
0.25 × 6 → 25 × 6 = 150. Two decimal places in all, so the answer is 1.50.
Example 3
Multiplying by a number less than 1 makes the result smaller: 8 × 0.5 = 4. That surprises people who expect multiplication to always grow a number.
Practice questions
- Multiply 2.5 × 1.3.
- Multiply 0.6 × 0.07.
- Estimate 4.9 × 3.1, then compute it exactly.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Multiplicación de decimales
Multiplica como si no hubiera puntos decimales, luego cuenta cuántos lugares decimales hay en AMBOS factores juntos y coloca esa cantidad en el resultado.
Ejemplo 1: 1.2 × 0.4 → 12 × 4 = 48. Un lugar decimal + un lugar decimal = dos lugares, entonces 0.48.
Ejemplo 2: 0.25 × 6 → 25 × 6 = 150. Dos lugares decimales en total, así que la respuesta es 1.50.
Ejemplo 3: Multiplicar por un número menor que 1 hace el resultado más pequeño: 8 × 0.5 = 4. Eso sorprende a quien espera que multiplicar siempre agrande un número.
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