Adding and Subtracting within 100
Aligned to 2.NBT.B.5 — Common Core State Standards for Mathematics.
What this lesson teaches
Add and subtract two-digit numbers by working with tens and ones separately, regrouping (carrying or borrowing) when needed.
Worked examples
Example 1
47 + 38: add ones 7+8=15 (write 5, carry 1 ten); add tens 4+3+1=8. Answer: 85.
Example 2
62 − 27: you cannot take 7 from 2, so borrow a ten — 62 becomes 5 tens and 12 ones. Now 12−7=5 and 5−2=3. Answer: 35.
Example 3
40 + 25: no regrouping is needed. Ones 0+5=5, tens 4+2=6. Answer: 65.
Practice questions
- Solve 56 + 27.
- Solve 63 − 28.
- Why do we 'carry' when the ones add to more than 9?
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
Suma y resta hasta 100
Suma y resta números de dos dígitos trabajando por separado con las decenas y las unidades, reagrupando (llevando o pidiendo prestado) cuando sea necesario.
Ejemplo 1: 47 + 38: suma las unidades 7+8=15 (escribe 5 y lleva 1 decena); suma las decenas 4+3+1=8. Resultado: 85.
Ejemplo 2: 62 − 27: no puedes quitarle 7 al 2, así que pide prestada una decena — 62 se convierte en 5 decenas y 12 unidades. Ahora 12−7=5 y 5−2=3. Resultado: 35.
Ejemplo 3: 40 + 25: no hace falta reagrupar. Unidades 0+5=5, decenas 4+2=6. Resultado: 65.
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