Week 06 · Two steps and patterns
Tuesday
Does it make sense?
// Solve, estimate and look for patterns
⏱ about 15 min
Tuesday: Does it make sense?
Oliver peers at a page in his notebook.
"Bennie, I added 48 and 31. I wrote 179."
"Something about it bothers me."
Bennie leans closer. "Let us round to check."
"48 is close to 50, and 31 is close to 30."
"50 + 30 = 80. So the answer should be about 80."
Oliver hoots softly. "Indeed! 179 is far too big."
Learn it: estimate to check
Round each number to the nearest ten.
48 rounds to 50, because 48 is closer to 50 than to 40.
31 rounds to 30. 50 + 30 = 80.
The exact answer is 48 + 31 = 79. That is close to 80.
An answer far from the estimate needs a second look.
ROUND FIRST
- Read the question.
- Tap your answer.
Round 48 to the nearest ten.
Round 31 to the nearest ten.
Round 267 to the nearest hundred.
Round 312 to the nearest hundred.
Round 75 to the nearest ten.
ESTIMATE
- Read the question.
- Tap your answer.
About how much is 48 + 31? Round each number to the nearest ten.
About how much is 62 + 29? Round each number to the nearest ten.
About how much is 89 - 42? Round each number to the nearest ten.
About how much is 312 + 196? Round each number to the nearest hundred.
About how much is 705 - 289? Round each number to the nearest hundred.
IS IT REASONABLE?
- Read the question.
- Tap your answer.
Oliver says 48 + 31 = 179. Is that reasonable?
Hazel says 62 + 29 = 91. Is that reasonable?
Riley says 312 + 196 = 708. Is that reasonable?
Lucy says 705 - 289 = 416. Is that reasonable?
Donnie says 91 - 38 = 13. Is that reasonable?
Estimate a two-step problem
Bennie picks 58 apples and then 33 more. He gives away 19.
Estimate: 60 + 30 - 20 = 70.
Exact: 58 + 33 - 19 = 72. That is close to 70.
SOLVE AND CHECK
- Read the question.
- Tap your answer.
Bennie picks 58 apples, then 33 more. He gives away 19. How many now?
Oliver must read 124 pages, then 145 more. He has read 60. How many pages are left?Riley has 7 bags of 9 stones. He uses 21 for a path. How many are left?
Estimate first, then check the exact answer.
| Sentence | True or false? |
|---|---|
| 48 + 31 = 79 | ? |
| 62 + 29 = 81 | ? |
| 312 + 196 = 508 | ? |
| 89 - 42 = 47 | ? |
WHY THIS EXERCISE62 + 29 is 91, close to the estimate 90.
Try it
Count the steps from your bed to the door.
Count the steps from the door to the kitchen.
Estimate the total by rounding. Then add exactly.
Is your exact answer close to your estimate?
Count the steps from the door to the kitchen.
Estimate the total by rounding. Then add exactly.
Is your exact answer close to your estimate?
Draw a number line from 40 to 50. Mark 48 and show where it rounds.
Wise checking! Tomorrow Oliver shows us patterns in the times table.