Setting up a subtraction problem

The principle

As with addition, the two numbers are aligned from the right, with the larger number (the minuend) above the smaller one (the subtrahend). Subtraction is carried out column by column, starting with the ones.

Simple case, without borrowing

587 - 254:

• Units: 7 - 4 = 3
• Tens: 8 - 5 = 3
• Hundreds: 5 - 2 = 3

Answer: 587 - 254 = 333

Case involving borrowing (carry-over)

When the top number is smaller than the bottom one, you cannot subtract directly: you must borrow 1 ten from the next column (you add 10 to the top number, and subtract 1 from the next number above it).

Example: 604 - 258

• Units: 4 - 8, impossible. We borrow 1 ten: 14 - 8 = 6. The top tens column loses 1 (so 0 itself becomes the borrower).
• Tens: 0 becomes 10 after borrowing from the hundreds, but we already have to give back 1 -> 10 - 1 = 9, then 9 - 5 = 4
• Hundreds: 6 becomes 5 (because we’ve borrowed) -> 5 - 2 = 3

Result: 604 – 258 = 346

Checking your answer

A useful tip: you can check a subtraction by adding the result to the number being subtracted. Here, 346 + 258 should equal 604.

Pitfalls to avoid

• Subtracting the smaller number from the larger one without following the correct order (for example, doing 8 - 4 instead of 4 - 8 with borrowing): this completely changes the answer.
• Forgetting to subtract 1 from the next column after borrowing.
• Misaligning the numbers when they are not the same length.