Grade 3 · Unit 1: Number and place value

Subtracting 3-digit numbers

Exchange when you need to.

Seats left

A hall has 524 seats. 286 are full. How many are empty? Estimate: 500 − 300 = 200.

Exchanging twice

Ones: 4 − 6? Exchange a ten: 14 − 6 = 8. Tens: now 1 − 8? Exchange a hundred: 11 − 8 = 3. Hundreds: 4 − 2 = 2. Answer: 238.

Zeros in the way

There are no tens to exchange in 403. Exchange 1 hundred for 10 tens first. Then 1 ten for 10 ones. 13 − 7 = 6, 9 − 5 = 4, 3 − 1 = 2. Answer: 246.

Check with addition

Use the inverse to check. Add the answer to the number you took away. You should get the number you started with.

Four-digit numbers

The column method works for 4-digit numbers too. Line up thousands, hundreds, tens and ones. Check: 7003 − 2378 = 4625 ✓

What I learnt

• I can subtract 3-digit numbers in columns.
• I can exchange across a zero.
• I can check with addition.