Stack It and Subtract!

Imagine you have 47 stickers. You give some away and have 23 left. How many did you give away? You need to subtract! Before we learn a new method, try these quick subtractions in your head: 9 − 4, 15 − 6, 30 − 10. Write your answers down.

Column subtraction is a written method that helps you subtract big numbers without getting muddled. You stack — that means you write — the numbers on top of each other in columns. Here is the key rule: always line up the digits by their place value. The ones digits (units) go in the right column, and the tens digits go in the left column. Step 1 — Write the larger number on top and the smaller number below it. Draw a line underneath. Step 2 — Start with the ones column (right side). Subtract the bottom digit from the top digit. Step 3 — Move to the tens column (left side). Subtract the bottom digit from the top digit. Step 4 — Write each answer below the line in the correct column. Sometimes the top ones digit is smaller than the bottom ones digit. In that case you need to exchange. Exchanging means you take 1 ten from the tens column and swap it for 10 ones. Add those 10 extra ones to your ones column so the top number is big enough to subtract from. Then remember the tens column now has one fewer ten. Worked example — 63 − 28: 6 3 − 2 8 ───── Ones column: 3 − 8. The top digit (3) is smaller than the bottom (8), so we exchange. We take 1 ten from the 6 tens, making it 5 tens. We add 10 to the 3 ones, making 13 ones. Now: 13 − 8 = 5. Write 5 in the ones column. Tens column: 5 − 2 = 3. Write 3 in the tens column. Answer: 63 − 28 = 35. Always check your answer makes sense. 35 is less than 63, so that looks right!