3 digit addition
What is the sum of 243, 132, and 157?
532
Subtract 382 - 148 mentally. Which of the following should you do first to find the difference?
- add 2 to 148 and add 2 to 382
- add 2 to 148 and subtract 2 from 382
- Subtract 8 from 148 and subtract 2 from 382
- Subtract 12 from 382 and add 12 to 148
add 2 to 148 and add 2 to 382
Find a reasonable estimate for the sum of 171 and 69. Select all that apply. (3)
175 + 70 = 245
100 + 60 = 160
170 + 70 = 240
175 + 75 = 250
130 + 70 = 200
175 + 70 = 245
170 + 70 = 240
175 +75 = 250
Look at the sums in the shaded column. Look at the addends. What pattern do you see?
(go to slides)
The sum is always the same as one of the addends. This is because a number plus 0 always equals that number.
Select all the equations that are true. (4)
- 32+56+10=10+56+32
- (49+28)+5=49+(28+5)
- 56+890=890+56
- 82+0=82
- 45+27=27+35
- 32+56+10=10+56+32
- (49+28)+5=49+(28+5)
- 56+890=890+56
- 82+0=82
Use mental math to add 332 and 154. Which of these shows how to break apart the numbers into hundreds, tens, and ones.
- Break 332 into 320 + 12. Break 154 into 125 +29
- Break 332 into 300 + 16 + 16. Break 154 into 100 + 27 +27
- Break 332 into 300 + 30 + 2. Break 154 into 100 + 50 + 4
Break 332 into 300 + 30 + 2. Break 154 into 100 + 50 + 4
Use mental math to find 634 - 528.
106
Estimate the difference of 765 and 333.
770 - 330 = 440
What addition equation can be used to check the answer for 456-342=114?
114+342=456
Find the sum of 350, 62, and 199.
549
Explain how to use mental math to find 620-278.
342
Look at the table in the slides
BCAD
169-57=112
How can you check your work using inverse operations?
57+112=169
Consider the sum of 123, 201, and 387. Estimate by rounding to the nearest 10.
123//120
201//200
387//390
120+200+390=710
Subtract 341-97 mentally. First add 3 to 97 to get 100. What should the next step be?
What is the answer of 341-97?
add 3 to 341. The difference is 244.
Estimate the sum of 405 and 385 by rounding to the nearest hundred.
400+400=800
How can you check the answer for 693-231=462
add 462 + 231 = 693
Look at table in slides.
668 // 700
404 // 400
649 // 600
489 //500
Consider the equation 360 = ___ + 84.
Use the bar diagram to represent the equation & solve it.
360-84=276
276+84=360