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
The lesson
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.
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.