Adding within 100
Add within 100 using strategies based on place value, including adding a two-digit and one-digit number, and a two-digit and a multiple of 10
What a learner can do afterwards
- Calculate 46 + 7 using place value (46 + 4 + 3 = 53)
- Calculate 38 + 40 = 78 using tens understanding
- Relate the strategy to a written method and explain the reasoning
1 · Read
You already know how to split a two-digit number into tens and ones. You can use that trick to add bigger numbers too. Keep the tens steady and work out the ones first.
Try 46 + 7. The 46 has 4 tens and 6 ones. First jump to the next ten: 46 + 4 = 50. That uses up 4 of your 7. There are 3 left, so 50 + 3 = 53. So 46 + 7 = 53.
If you write 46 and 7 on top of each other to add them, the 7 goes under the 6, because both are ones. Lining up the columns is the same idea as keeping tens and ones apart in your head.
Split the numbers into tens and ones, add each part, then put them back together.
More to read
Adding and Subtracting Within 100 Using Place Value Strategies (Grade 2)
Adding within 100 uses place value. For 46 + 7, split 7 into 4 and 3. Add 46 + 4 to reach 50. Then add 3 more to get 53.
Add and subtract within 100: FAQ
Tens help a lot within 100. 38 + 40 means 3 tens plus 4 tens. That is 7 tens. With 8 ones that is 78. When you add tens, the ones stay still. Say the tens jump aloud.
Properties of addition
Written methods match the blocks. Line up tens under tens and ones under ones. Add ones first, trade 10 ones for a ten if needed. Then add tens.
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.