321 on the frame: three hundreds, two tens and one one.
The big ideaThe top row counts hundreds. Add hundreds, tens and ones, each on their own.
How it works
A third row counts hundreds. Ten ones make a ten, and ten tens make a hundred, so one bead on the top row is worth a hundred.
Add the hundreds, the tens and the ones, each row on its own, just as before.
A row with no beads still counts, as zero. The zero holds the place, or 406 would look like 46.
Check that your answer makes sense: 300 and 100 make 400, plus a bit more.
The answer, 457: four hundreds, five tens and seven ones.
Example 1: Three rows
Put 321 on the frame: three hundreds, two tens and one one.
Hundreds: 3 + 1 = 4.
Tens: 2 + 3 = 5.
Ones: 1 + 6 = 7.
321 + 136 = 457
4 hundreds, 5 tens and 7 ones is 457.
Example 2: Only the ones move
Put 245 on the frame.
Add 4 ones: 5 + 4 = 9.
The hundreds and tens rows do not change.
245 + 4 = 249
2 hundreds, 4 tens and 9 ones is 249.
Example 3: An empty row
407 has no tens, so the tens row starts empty.
Hundreds: 4 + 1 = 5.
Tens: 0 + 8 = 8.
Ones: 7 + 2 = 9.
407 + 182 = 589
5 hundreds, 8 tens and 9 ones is 589.
Example 4: Add again
A third school brings 212 more books, so start from 457.
Hundreds: 4 + 2 = 6.
Tens: 5 + 1 = 6.
Ones: 7 + 2 = 9.
457 + 212 = 669
6 hundreds, 6 tens and 9 ones is 669.
Words to know
hundreds row
The top row of a three-row frame. Each bead is worth a hundred.
tens row
The middle row. Each bead is worth ten.
ones row
The bottom row. Each bead is worth one.
place
Where a digit sits: hundreds, tens or ones.
Watch out
Read the rows from the top: hundreds, tens, ones. Not the other way round.
A row with no beads is not missing. It is a zero, and it holds the place.
With three rows you can add all the way to 999.
Try it
What is 132 + 246?
What is 214 + 325?
What is 302 + 156?
Which has a zero in the tens place, 406 or 46?
Answers: 1. 378 · 2. 539 · 3. 458 · 4. 406
Try at homeAsk a grown-up to help you count a small shelf of books and a second shelf, up to about two hundred each. Add the hundreds first, then the tens, then the ones, and see whether the total makes sense.
For grown-upsUse real books, cards or coins in piles of a hundred, a ten and singles, and let your child add one pile type at a time.
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