lesson
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Imagine a frog sitting on number 24 along a sidewalk. If that frog takes two giant super-hops of 10, where will it land?
An open number line is an empty straight line where you get to sketch your own numbers and hops.
📊Interactive diagram
What happens to a two-digit number when you add ten to it?
Jumping by Tens
A multiple of ten is any number made of full groups of ten, such as 10, 20, 30, or 40.
This rule is the place-value invariant: each jump of +10 increases the digit in the tens place by 1, while the ones digit stays exactly the same (such as 34→44→54).
📊Interactive diagram
At 24, you have 2 tens and 4 ones. Adding one ten gives 3 tens and 4 ones (34), and one more ten makes 4 tens and 4 ones (44).
To keep tracking visible and organized, follow the dual labeling protocol: record the action jump above the arc (+10) and the landing landmark number below the line.
How would you solve an addition problem when the number to add has three tens, like 30?
Adding Thirty: Three Hops
Let's solve 35+30 using our number line. Since 30 is equal to 3 tens, we can make 3 jumps of ten forward from 35.