Use Partial Sums/Differences to Add and Subtract
What 2 numbers represent the ones place in this equation?
356 + 123
6 and 3
Why would you round each number and estimate the sum before you find the exact sum?
It helps you check to see if your exact answer is reasonable.
356 - 189
In this example, how do you know if regrouping is necessary?
In the ones place, 6 + 9 = 15 which is bigger than 9, therefore it needs to be regrouped.
64 + 42 + 88 = ?
194
Mr. Lee had $385 in the bank. Then he spent $242. Ms. Davis had $685 in the bank and then spent $542. Who has more money left? Conjecture: They both have the same amount of money left.
What’s the first step to solving this?
Figure out how much money both Mr. Lee and Ms. Davis have left in the bank.
Break apart 185 + 613 into hundreds, tens and ones.
100 + 80 + 5 = 185
600 + 10 + 3 = 613
Estimate by rounding to the nearest ten, then solve 163 + 50. Compare the answers to find if your answer is reasonable.
160 + 50 = 210
163 + 50 = 213
The answers are close, therefore 213 is a reasonable answer.
Subtract: 374 - 176 = ?
198
510 + 45 + 27 = ?
582
Mr. Lee had $385 in the bank. Then he spent $242. Ms. Davis had $685 in the bank and then spent $542. Who has more money left? Conjecture: They both have the same amount of money left.
After we find how much each person has left, what is our next step?
Compare each amount left in the bank and decide which one is greater or if they are the same.
Subtract 465 - 351 by breaking down each number into hundreds, tens and ones.
400 - 300 = 100
60 - 50 = 10
5 - 1 = 4
100 + 10 + 4 = 114
Estimate by rounding to the nearest ten, then solve 418 + 351. Compare the answers to find if your answer is reasonable.
418 + 351 = 769
Subtract: 856 - 219 = ?
637
602 + 125 + 231 = ?
958
Mr. Lee had $385 in the bank. Then he spent $242. Ms. Davis had $685 in the bank and then spent $542. Who has more money left? Conjecture: They both have the same amount of money left.
Is the conjecture correct? Draw a diagram to justify your answer.
Yes, you could use a number line or a bar diagram to show this.
Add 730 + 168 by breaking down each number into hundreds, tens and ones.
700 + 100 = 800
30 + 60 = 90
0 + 8 = 8
800 + 90 + 8 = 898
Estimate by rounding to the nearest ten, then solve 516 + 325. Compare the answers to find if your answer is reasonable.
520 + 330 = 850
516 + 325 = 841
The answers are close, therefore 841 is a reasonable answer.
Estimate by rounding to the nearest ten, then subtract.
526 - 238 = ?
530 - 240 = 290
526 - 238 = 288
246 + 54 + 233 + 205 = ?
738
Some musicians set goals for the number of minutes they want to practice before a concert, which is 5 days away. How many more minutes does Aria need to practice to reach her goal?
Aria Dexter
Minutes Practiced: 608 612
Goal: 700 650
700 - 608 = 82
Subtract 755 - 315 by breaking down 315 into hundreds, tens and ones.
755- 300 = 455
455 - 10 = 445
445 - 5 = 440
To add 546 + 327, would you need to regroup? Explain.
Yes, 6 + 7 = 13, which is greater than 9.
Estimate by rounding to the nearest ten, then subtract.
629 - 453 = ?
630 - 450 = 180
629 - 453 = 176
125 + 35 + 124 + 239 = ?
523
Some musicians set goals for the number of minutes they want to practice before a concert, which is 5 days away. Who needs more minutes to reach their goal, Aria or Dexter?
Aria Dexter
Minutes Practiced: 608 612
Goal: 700 650
82 > 38, Aria needs more minutes to reach her goal than Dexter.