Adding or Subtracting 10 and 100

Aligned to 2.NBT.B.8 — Common Core State Standards for Mathematics.

What this lesson teaches

When you add 10, only the tens digit changes. When you add 100, only the hundreds digit changes. Do it in your head.

Example 1

Start with 254. Add 100: the hundreds go from 2 to 3, so 254 + 100 = 354.

Example 2

Start with 683 and subtract 10: the tens go from 8 to 7, so 683 − 10 = 673.

Example 3

Start with 940 and add 100: the hundreds go from 9 to 10, so the number becomes 1,040.

Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.

Cuando sumas 10, solo cambia el dígito de las decenas. Cuando sumas 100, solo cambia el dígito de las centenas. Hazlo de memoria.

Ejemplo 1: Empieza con 254. Suma 100: las centenas pasan de 2 a 3, entonces 254 + 100 = 354.

Ejemplo 2: Empieza con 683 y resta 10: las decenas pasan de 8 a 7, entonces 683 − 10 = 673.

Ejemplo 3: Empieza con 940 y suma 100: las centenas pasan de 9 a 10, así que el número se vuelve 1,040.

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