When you add tens, you only add to the rods. The cubes are untouched.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Watch the ones
12 + 30. The 2 ones stay. 1 ten and 3 tens make 4 tens. The answer is 42.
Rods go with rods. Cubes go with cubes.
The ones are untouched
24 + 10 = 34. The 4 never moved, because you added whole tens and never touched the loose pile.
Why this is worth noticing
It means you can add tens instantly, at any size of number, without counting anything.
Step 2: Try It Yourself
Tap and try it out.
First number
and Add tens
Altogether
Tens
3
Ones
2
12 + 20 = 32
1 tens and 2 tens make 3 tens. Ones go with ones.
Step 3: Watch an Example
One step at a time.
Watch Ana Add Tens
Ana works out 14 + 20.
- Step 1
She looks at the cubes. There are 4, and nothing joins them.
Step 4: Your Turn
Practice makes it stick.
Two Bags
Problem 1 of 1
Leo has 13 marbles. He finds a bag of 20. How many?
marbles
Add the Tens Only
1 of 3
15 + 10 = ?
2 of 3
12 + 20 = ?
3 of 3
17 + 20 = ?
Step 5: Quick Check
Show what you know.
Question 1 of 2
16 + 20 = ?
Question 2 of 2
When you add 10, does the ones digit change?
What You Learned
- Tens join the tens. Ones stay as they are.
- 12 + 30 = 42.
- Only the tens digit changes.