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

Round to the Nearest Hundred Sprint

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

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

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

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

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

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

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 =

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?

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 =

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?

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

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?

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.

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?

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?

496 - 209 496 - 209 496 - 209 496 - 209 496 - 209 JUST THE PART TENS TO HUNDRED HUNDREDS TENS 496 - 209 496 - 209 496 - 209 500 – 200 = 300 500 – 210 = 290 496– 200= 296 JUST THE PART TO TENS 496 - 209 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. 496 - 209 287

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?

PROBLEM SET