Adding Tens and Two-Digit Plus One-Digit

When you are in first grade, you start adding bigger numbers! Today, we will learn how to add tens together, and how to add a one-digit number to a two-digit number. The best part? We won't need to do any carrying or regrouping.

Adding Tens Together

Adding numbers ending in zero (like 10, 20, 30) is just like adding single digits.

Let's look at $30 + 40$:

1. Look at the first digits: $3$ and $4$.
2. Add them together: $3 + 4 = 7$.
3. Put the zero back at the end.

$30 + 40 = 70$

If you have 3 tens and add 4 tens, you get 7 tens!

Adding a Two-Digit Number and a One-Digit Number

What happens when we add a small number to a bigger number, like $23 + 5$?

1. Look at the ones place. In $23$, the ones digit is $3$. The other number is $5$.
2. Add the ones together: $3 + 5 = 8$.
3. The tens place stays the exact same. In $23$, the tens digit is $2$.

Put them together:

$23 + 5 = 28$

Adding a Two-Digit Number and a Multiple of Ten

Sometimes you will add a number like $20$ to a two-digit number, like $45 + 20$.

1. Look at the tens place. In $45$, the tens digit is $4$. In $20$, it's $2$.
2. Add the tens together: $4 + 2 = 6$.
3. The ones place stays the exact same. In $45$, the ones digit is $5$. Adding $0$ to it keeps it as $5$.

Put them together:

$45 + 20 = 65$

Quick Practice

Try these out using the steps above:

• $50 + 30 = 80$ (Because $5 + 3 = 8$)
• $41 + 6 = 47$ (Because $1 + 6 = 7$)
• $34 + 10 = 44$ (Because $3 + 1 = 4$)