The big ideaPicture the beads. Add tens first, then ones. A full ones row trades for a ten.
How it works
Picture the first number on the frame. Add the tens first, then the ones.
Tens go on the tens row, so only that row moves.
If the ones row fills up, trade ten ones for one ten.
Check your answer on a real frame or on paper.
The plan for adding in your head.57 + 8: the ones row filled and traded, leaving sixty-five.
Example 1: Adding tens: 31 + 20
Picture 31: three tens and one one.
Twenty is two tens, so only the tens row moves.
Three tens and two tens make five tens.
31 + 20 = 51.
31 + 20: five tens and one one.
Example 2: Adding ones: 51 + 6
Picture 51.
Six more ones slide across: one and six make seven.
51 + 6 = 57.
Example 3: A trade: 57 + 8
Seven ones are across, with room for only three more.
Three of the eight fill the row, so ten ones trade for one ten.
Five more ones slide across after the trade.
Six tens and five ones: 57 + 8 = 65.
Example 4: Tens, then a trade: 27 + 15
Picture 27.
Add the ten first: one more ten makes 37.
Add the five ones: seven and five make 12, so ten ones trade up.
Four tens and two ones: 27 + 15 = 42.
Example 5: No trade: 52 + 23
Add the tens: five tens and two tens make seven tens.
Add the ones: two and three make five.
The row has room, so nothing trades: 52 + 23 = 75.
Words to know
mental
Done in your head, with a picture of the frame.
trade
Ten ones become one ten.
tens row
The row above the ones row. Tens go here.
ones row
The bottom row. It counts ones.
Watch out
Tens go on the tens row, not the ones row.
A full ones row must trade: twelve ones is one ten and two ones.
Add the tens first, then the ones.
Not every sum needs a trade. 52 + 23 has none.
Try it
What is 45 + 20?
Does 36 + 7 need a trade?
What is 48 + 5?
What is 64 + 29?
Answers: 1. 65 · 2. Yes · 3. 53 · 4. 93
Try at homeAsk a grown-up to say a sum to ninety-nine, like thirty-four plus twenty-five. Close your eyes and picture the frame. Say your answer, then check on a real frame or on paper. Swap turns!
For grown-upsSay a sum to ninety-nine, like 34 + 25. Your child shuts their eyes, pictures the frame and says the answer, then checks on a real frame or on paper. Swap turns.
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