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Ages 7+ · Abacus · Taking away
Taking from 100
hundredstensones100
100 on the frame: one bead on the top row.
The big ideaTo take from one hundred, open the hundred, then open a ten.

How it works

One hundred has no loose tens or ones on the frame, so to take from it, open the hundred first.

Open the hundred, and the tens row fills with ten beads. Then open one ten: nine tens stay and the ones row fills up.

Now both rows are ready. Take away the tens, then the ones.

It works because a hundred is nine tens and ten ones. Nothing is lost.

hundredstensones
The hundred and a ten are open: nine tens and ten ones.

Example 1: 100 take away 46

  1. Open the hundred, then open a ten: 9 tens and 10 ones.
  2. Take away 4 tens: 9 - 4 = 5 tens.
  3. Take away 6 ones: 10 - 6 = 4 ones.
  4. 100 - 46 = 54
hundredstensones54
5 tens and 4 ones stay: 54.

Example 2: 100 take away 38

  1. Open the hundred and a ten: 9 tens and 10 ones.
  2. Tens: 9 - 3 = 6. Ones: 10 - 8 = 2.
  3. 100 - 38 = 62
hundredstensones62
6 tens and 2 ones stay: 62.

Example 3: Only a few

  1. Take just 4 from 100. You still open the hundred and a ten: 9 tens and 10 ones.
  2. Take away 4 ones: 10 - 4 = 6 ones. The 9 tens stay.
  3. 100 - 4 = 96
hundredstensones96
9 tens and 6 ones stay: 96.

Example 4: The pattern

  1. In 100 - 46, the tens 4 and 5 make 9.
  2. The ones 6 and 4 make 10.
  3. What you take away and what stays share those tens and those ones.
  4. Check by adding back: 54 + 46 = 100

Words to know

open the hundred
Slide the hundred bead down so the tens row fills with ten beads.
open a ten
Slide one tens bead down so the ones row fills with ten beads.
borrow
Trade one bead down for ten on the row below.
hundred
Ten tens, one bead on the top row.

Watch out

Try it

  1. What is 100 - 37?
  2. What is 100 - 85?
  3. What is 100 - 65?
  4. After you open the hundred and a ten, how many tens and ones are on the frame?
Answers: 1. 63 · 2. 15 · 3. 35 · 4. 9 tens and 10 ones
Try at homeAsk a grown-up for ten stacks of ten coins or buttons, one hundred in all. Take some away, like thirty-seven. You will need to open a stack of ten to give the ones. Say how many tens and ones are left.
For grown-upsMake one hundred out of ten stacks of ten coins or buttons. Take some away, like 37, and let your child open a stack to give the ones.
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