Cogito
Grade 1 Math · Chapter 10 · Lesson 7
Adding to 100 With Place Value
Add bigger numbers by adding tens to tens.
10 problems · about 13 minutes · 1.NBT.C.4
What this lesson teaches
The child adds two-digit numbers within 100 by adding like units, with no new ten required.
- Add the tens, then add the ones.
- The method is the same at any size.
- 42 + 35 = 77.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Ten More, Ten Less to 100: Ten more than 66 is?
Answer 76
Why 6 tens became 7 tens.
Review — Comparing Numbers to 100: Which is greater, 38 or 41?
Answer 41
Why 41 has more tens.
Review — Counting to 120: What comes right after 104?
Answer 105
Why After 104 comes 105.
Review — Numbers to 100: How many ones are in 86?
Answer 6
Why 86 is 8 tens and 6 ones.
Warm Up
Straightforward practice. Get the method working first.
3 problems34 + 25 = ?
Answer 59
Why 5 tens and 9 ones is 59.
61 + 27 = ?
Answer 88
Why 8 tens and 8 ones is 88.
23 + 41 = ?
Answer 64
Why 6 tens, then 3 and 1.
Build It Up
The same ideas with more to keep track of.
1 problem52 + 36 = ?
Answer 88
Why 8 tens, then 2 and 6.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems45 + 30 = ?
Answer 75
Why The 5 stays.
Two Collections: Leo has 31 cards. Ana has 24. How many altogether?
Answer 55 cards
Why 31 + 24 = 55.