Sometimes you add three or four numbers, like the points in a game. Place value still works: add all the tens, add all the ones, then put them together. You already know Adding Two-Digit Numbers.
Por qué funciona
You can add numbers in any order and get the same total (Adding in Any Order). So you can gather all the tens first and all the ones first. Looking for ones that make 10 makes it even easier.
Ejemplo resuelto: Tens, then ones
Find $23 + 14 + 31 + 12$.
- Tens: $20 + 10 + 30 + 10 = 70$.
- Ones: $3 + 4 + 1 + 2 = 10$.
- $70 + 10 = 80$.
Respuesta: $80$
Ejemplo resuelto: Find a ten
Find $36 + 25 + 14$.
- 36 and 14 have ones that make 10: $6 + 4$.
- $36 + 14 = 50$.
- $50 + 25 = 75$.
Respuesta: $75$
Ejemplo resuelto: Lots of ones
Find $47 + 28 + 19 + 35$.
- Tens: $40 + 20 + 10 + 30 = 100$.
- Ones: $7 + 8 + 9 + 5 = 29$. That is 2 tens and 9 ones.
- $100 + 29 = 129$.
Respuesta: $129$
Idea clave
To add several numbers, add all the tens, add all the ones, then combine. Look for ones that make 10.
Error común
Leaving a number out, or forgetting that the ones can make two new tens. Check: touch each number as you add it, and see whether the ones add to more than 19.
Grown-up tip: Keep score in a board game and add up each player’s points together.