Cogito
Grade 2 Math · Chapter 4 · Lesson 3
Adding Past 100
Ten tens make a hundred, in the middle of a sum too.
10 problems · about 13 minutes · 2.NBT.B.5, 2.NBT.B.7
What this lesson teaches
The child adds two two-digit numbers whose total passes 100, composing a hundred.
- Ten ones make a ten. Ten tens make a hundred.
- The rule is the same at every place.
- Answers can go past 100.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Making a New Ten: 29 + 34 = ?
Answer 63
Why 5 tens and 13 ones becomes 6 tens and 3 ones.
Review — Adding With Place Value: 23 + 41 = ?
Answer 64
Why 23 + 41 = 64.
Warm Up
Straightforward practice. Get the method working first.
4 problems58 + 67 = ?
Answer 125
Why 58 + 67 = 125.
How many tens bundle into one hundred?
Answer 10
Why Ten tens make a hundred.
70 + 50 = ?
Answer 120
Why 12 tens.
63 + 54 = ?
Answer 117
Why 11 tens and 7 ones.
Build It Up
The same ideas with more to keep track of.
2 problems86 + 25 = ?
Answer 111
Why A new ten, then a new hundred.
92 + 45 = ?
Answer 137
Why 13 tens and 7 ones.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Sponsored Walk: Leo raised 75 pounds and Ana raised 60. How much did they raise together?
Answer 135 pounds
Why 75 + 60 = 135.
Two Boxes: A box holds 84 marbles and another holds 47. How many marbles in all?
Answer 131 marbles
Why 84 + 47 = 131.