Cogito
Grade 2 Math · Chapter 5 · Lesson 1
Adding and Subtracting Hundreds
Whole hundreds behave like single digits.
10 problems · about 11 minutes · 2.NBT.B.7
What this lesson teaches
The child adds and subtracts multiples of 100 within 1,000.
- A hundred is a unit you can count.
- 3 hundreds and 2 hundreds make 5 hundreds.
- Only the hundreds digit changes.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Two-Step Word Problems Within 100: 55 apples. 27 more arrive. 34 are sold. How many are left?
Answer 48
Why 55 + 27 = 82, and 82 − 34 = 48.
Review — Word Problems Within 100: 47 birds. 28 fly away. How many are left?
Answer 19
Why 47 − 28 = 19.
Warm Up
Straightforward practice. Get the method working first.
4 problems400 + 500 = ?
Answer 900
Why 400 + 500 = 900.
700 − 200 = ?
Answer 500
Why 700 − 200 = 500.
200 + 600 = ?
Answer 800
Why 2 and 6 hundreds.
500 + 500 = ?
Answer 1000
Why Ten hundreds.
Build It Up
The same ideas with more to keep track of.
2 problems800 − 300 = ?
Answer 500
Why 8 take 3 hundreds.
600 − 600 = ?
Answer 0
Why Every flat goes.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTwo Schools: One school has 300 pupils and another has 500. How many altogether?
Answer 800 pupils
Why 300 + 500 = 800.
The Fundraiser: A target of 900 pounds has 400 raised so far. How much is still needed?
Answer 500 pounds
Why 900 − 400 = 500.