Adding and subtracting (age 8+)
Add and subtract numbers with up to four digits using formal written methods of columnar addition and subtraction
What a learner can do afterwards
- Set out and solve a columnar addition with up to four-digit numbers
- Set out and solve a columnar subtraction with exchange across multiple columns
- Check the answer using estimation or inverse operations
The lesson
You already know how to carry and exchange with smaller numbers. Now you will use the exact same idea with numbers that have thousands, hundreds, tens, and ones. Line up the digits by place value, with the ones on the right, and work from right to left.
Subtract 4,301 − 2,658. Ones: 1 is smaller than 8, so you need to exchange. The tens digit is 0, so exchange a hundred for ten tens first, then exchange a ten for ten ones. Now: 11 − 8 = 3. Tens: 9 − 5 = 4. Hundreds: 2 − 6 is too small, so exchange a thousand for ten hundreds: 12 − 6 = 6. Thousands: 3 − 2 = 1. The answer is 1,643.
Always check your work. Round each number and estimate, or use the opposite operation. For 3,842 + 1,765, check with 5,607 − 1,765, which should give back 3,842.
Line up numbers by place value, carry or exchange when a column doesn't fit, and always check your answer.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.