Multiplying Big Numbers
Aligned to 5.NBT.B.5 — Common Core State Standards for Mathematics.
What this lesson teaches
The standard algorithm lets you multiply large numbers by breaking the second number into its places. Multiply by the ones, then by the tens, and so on, then add the parts together. Line up your place values carefully.
Worked examples
Example 1
Multiply 34 × 26. First 34 × 6 = 204. Next 34 × 20 = 680. Add the two parts: 204 + 680 = 884. So 34 × 26 = 884.
Example 2
Multiply 125 × 32. 125 × 2 = 250, and 125 × 30 = 3,750. Add: 250 + 3,750 = 4,000.
Example 3
Estimate first: 34 × 26 is about 30 × 30 = 900, so 884 is reasonable and 88 or 8,840 is not.
Practice questions
- Multiply 47 × 23.
- Multiply 312 × 15.
- Multiply 268 × 34 and show each partial product you added.
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
Multiplicar números grandes
El algoritmo estándar te deja multiplicar números grandes separando el segundo número en sus lugares. Multiplica por las unidades, luego por las decenas, y así, y después suma las partes. Alinea con cuidado los valores posicionales.
Ejemplo 1: Multiplica 34 × 26. Primero 34 × 6 = 204. Luego 34 × 20 = 680. Suma las dos partes: 204 + 680 = 884. Así, 34 × 26 = 884.
Ejemplo 2: Multiplica 125 × 32. 125 × 2 = 250 y 125 × 30 = 3,750. Suma: 250 + 3,750 = 4,000.
Ejemplo 3: Estima primero: 34 × 26 es como 30 × 30 = 900, así que 884 es razonable y 88 u 8,840 no lo son.
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