1. Module 2 Lesson 20
Estimate differences by rounding and apply to solve measurement word problems.

2. Round to the Nearest Hundred Sprint

3. End Rounding Sprint 2 minutes
This ‘sand timer’ will start on a mouse click anywhere on the slide. The ‘sand’ will drain from the top section to the lower section and when completed will show the word ‘End’.
To change the timings of this timer, you need to enter the animation settings, and change the timings for the Isosceles Triangles. There will be 2 that need changing (to the same amount) – one animates the top triangle emptying, whilst the other animates the bottom triangle filling.
When you change the timings these have to entered as a number of seconds.
End

4. Subtracting with measurements
SOLVE ON YOUR BOARDS USING THE STANDARD ALGORITHM
50 L – 28 L = _____
22 L

5. Subtracting with measurements
SOLVE ON YOUR BOARDS USING THE STANDARD ALGORITHM
450 L – 28 L = _____
422 L

6. Subtracting with measurements
SOLVE ON YOUR BOARDS USING THE STANDARD ALGORITHM
450 L – 228 L = _____
222 L

7. Subtracting with measurements
SOLVE ON YOUR BOARDS USING THE STANDARD ALGORITHM
604 L – 32 L = _____
572 L

8. Subtracting with measurements
SOLVE ON YOUR BOARDS USING THE STANDARD ALGORITHM
604 g – 132 g = _____
472 g

9. Estimate 362 – 189 by rounding 400 200 362 – 189 =
What is 362 rounded to the nearest hundred?
400
What is 189 rounded to the nearest hundred?
200
Let’s write our rounded estimates directly below
The original numbers.
362 – 189 =

10. Time to solve our estimate and the actual problem.
WHAT IS THE ANSWER TO OUR ESTIMATE?
362
- 189
400
200
173
200
What is the answer to our actual problem?

11. Estimate 362 – 189 by rounding 360 190 362 – 189 =
What is 362 rounded to the nearest ten?
360
What is 189 rounded to the nearest ten?
190
Let’s write our rounded estimates directly below
The original numbers.
362 – 189 =

12. Time to solve our estimate and the actual problem.
WHAT IS THE ANSWER TO OUR ESTIMATE?
362
- 189
360
190
173
170
What is the answer to our actual problem?

13. We rounded to the nearest 10 and 100…Is there another way we could round these numbers so it is EASY to subtract?
In 362 – 189. What Minuend is the WHOLE (What we are starting with) and which is the PART (what we’re taking away)?
362 is the WHOLE
189 is the PART
Why don’t we round just the PART? Why is that a better number to round to 200, than rounding 362 to 400?
BECAUSE 189 is closer to 200 than 362 is to 400. It’s easier MENTAL MATH

14. Let’s look at all our rounded answers
Rounded to the HUNDREDS
Rounded to the TENS
362
- 189
400
362
- 189
360
200
190
173
200
173
170
362
- 189
362
WHICH ONE IS CLOSEST TO THE ACTUAL?
200
Just rounding the PART
WHICH ONE HAD THE EASIEST MENTAL MATH ?
173
162
WHICH COMBINED EASY MENTAL MATH WITH A GOOD ESTIMATE?

15. Analyze the estimations to four different subtraction problems.
349
-154
WHOLE
349
-149
351
-154
351
-149
PARTS
195
200
197
202
WHAT DO YOU NOTICE ABOUT DIFFERENCES?
LETS LOOK AT THE PARTS.
WHAT DO YOU NOTICE?
THEY ARE ALL CLOSE TO 150.
LETS LOOK AT THE WHOLE/TOTALS.
WHAT DO YOU NOTICE?
THEY ARE ALL CLOSE TO 350.

16. Let’s round to the nearest hundred
349
-154
349
-149
351
-154
351
-149
300
-200
300
-100
400
-200
400
-100
195
200
197
202
100
300
200
200
WHAT DO YOU NOTICE ABOUT OUR ROUNDED DIFFERENCES/ANSWERS?
SOME ARE GOOD ESTIMATES AND SOME ARE NOT.
WHAT MAKES THE DIFFERENCE?
LOOK AT IF WE ROUNDED THE NUMBER UP OR DOWN!
WHICH ESTIMATES ARE CLOEST TO THE REAL ANSWERS?
WHY?

17. 496 - 209 Think about how to round to get the Most precise estimate.
IS IT BETTER TO:
Round to the hundreds?
Round JUST the Part?
Round to the Tens?

18. 496 - 209 496 - 209 496 - 209 496 - 209 496 - 209 JUST THE PART TENS
TO HUNDRED
HUNDREDS
TENS
500 – 200 = 300
500 – 210 = 290
496– 200= 296
JUST THE PART
TO TENS
WHAT DO YOU NOTICE ABOUT OUR ESTIMATES?
They are all pretty close to the real answer.
496– 210= 286
ACTUAL
WHY WERE THEY ALL SO CLOSE TO EACHOTHER?
Because the numbers we started with are very close to the estimated numbers.
287

19. SHOW WHAT YOU KNOW PROBLEM!
Millie’s fish tank holds 403 liters of water. She empties out 185 liters of water to clean the tank. How many liters of water are left in the tank?
Estimate how many liters are in the tank.
Estimate how many liters are in the tank a different way.
How many liters are actually left in the tank?
Is your answer reasonable? Which estimate is closer?

20. PROBLEM SET