Mental addition and subtraction (age 9+)
Add and subtract numbers mentally with increasingly large numbers, using place-value knowledge and derived facts
What a learner can do afterwards
- Mentally calculate 45,000 + 8,000
- Mentally subtract 3,200 from 10,000 by counting up
- Use near-doubles: 2,500 + 2,600 = 5,100
1 · Read
You already know how to break numbers apart by place value and use facts you know to find new ones. Now you use those same tricks on bigger numbers, like thousands.
Kai adds 45,000 and 8,000. He knows 45,000 is 45 thousand and 8,000 is 8 thousand. He just adds the thousands: 45 + 8 = 53. So 45,000 + 8,000 = 53,000.
Priya adds 2,500 and 2,600. She knows the double 2,500 + 2,500 = 5,000. Since 2,600 is 100 more than 2,500, she adds that extra 100 too: 5,000 + 100 = 5,100.
Look for the round numbers hiding inside a big number. Breaking it into thousands, hundreds, or a double you already know makes the whole problem easier.
Break big numbers into place value chunks, count up to subtract, and use near-doubles to add fast in your head.
More to read
Use place value understanding to subtract efficiently using take from a hundred
Subtracting near a hundred is quick with a hop. To find 100 minus 47, jump 3 to reach 50, then 50 more to 100. The total hop is 53.
Number lines turn this into a game. Mark your jumps and add them for the answer.
Use place value understanding to subtract efficiently using take from a ten
Taking from ten helps with subtraction. If you know 10 minus 7 is 3, then 20 minus 7, 30 minus 7 and 70 minus 7 follow the same pattern with tens attached.
Practise pairs that make ten until they pop.
Adding and subtracting within 1,000: FAQ
Adding within 1,000 stacks hundreds, tens and ones in columns. Add each column from the right and carry tens forward. Subtraction mirrors it with exchanges.
Estimate with round hundreds first. A quick check catches most slips.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
17 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.