Week 08 · Subtract within 100
Wednesday
Why it works
// Take away tens and ones
⏱ about 15 min
Wednesday: Why it works
Donnie looks at his answer and tilts his head.
"I found 63 - 25 = 38. How can I be sure?" he asks.
Oliver the Owl peeks down from a branch.
"Adding and subtracting are partners," Oliver says.
"Add 38 and 25. If you get 63, your answer is right!"
Learn it: check with addition
Subtracting takes a part away from the whole.
Adding puts the parts back together.
63 - 25 = 38.
Check: 38 + 25 = 63. It matches!
Breaking a ten works because one ten is ten ones.
The number stays the same. Only the blocks change.
WHICH SUM CHECKS IT?
- Read the question.
- Tap your answer.
63 - 25 = 38. Which sum checks it?
74 - 31 = 43. Which sum checks it?
90 - 46 = 44. Which sum checks it?
FIND THE MISSING PART
- Read the question.
- Tap your answer.
25 + ? = 63
47 + ? = 80
19 + ? = 55
36 + ? = 91
WHY DOES IT WORK?
- Read the question.
- Tap your answer.
Why can we break a ten into ten ones?
52 is 5 tens and 2 ones. It is also:
Does breaking a ten change the number?
One ten is the same as ten ones.
| Sentence | True or false? |
|---|---|
| We can check subtraction with addition. | ? |
| 4 tens and 12 ones is 52. | ? |
| Breaking a ten makes the number smaller. | ? |
WHY THIS EXERCISEBreaking a ten does not change the number.
Try it
Count 30 small things into 3 piles of 10.
Open one pile and spread it out.
Count them all again. Is it still 30?
Open one pile and spread it out.
Count them all again. Is it still 30?
Draw 52 as 4 tens and 12 ones.
Word Spot: miles, night, walked
Here are new sight words.
Look at each word. Say it. Spell it.
Miles: M-I-L-E-S.
Night: N-I-G-H-T.
Walked: W-A-L-K-E-D.
FIND THE WORD
- Listen to the word.
- Tap it.
Find the word you hear.
Find the word you hear.
Find the word you hear.
Find the word you hear.
FILL THE GAP
- Listen to the sentence.
- Tap the missing word.
The trail is two ___ long.
Many owls hunt at ___.
We ___ to the park.
Wonderful thinking! Tomorrow Chris tells a story about Donnie.