Transcript Adding or Subtractin..

MENTAL MATH
Addition and Subtraction by making
“nice numbers”
Strategy: Take one of the numbers in your question and
round it to the nearest tens or hundreds. These are
called “nice” numbers because they are easier to add
and subtract. Make sure you are only changing it less
than 10 from its original number. Once you get the
answer add or subtract the difference in your
rounded number.
Example #1: When adding and rounding you do the
opposite operation to your rounding.
463 + 297(+3)
463 + 300 = 763 (-3) =760
Example #2: When subtracting you do the same
operation as rounding.
Hint: To help remember both “subtract” and “same” start with the
letter S
669 – 304 669 – 300 (- 4) =
369 (- 4) = 365
Example #3:
532 + 328 530(-2) + 328 = 858
858 (+2) = 860
Practice with…
adding or subtracting
by rounding with nice
numbers…
521
+298
521 + 300 ( +2) = 821
821 (-2) = 819
838
- 599
838 - 600 ( +1) = 238
238 (+1) = 239
724
+103
724 + 100 ( -3) = 824
824 (+3) = 827
377
- 204
377- + 200 ( -4) = 177
177 (-4) = 173
558
- 497
558 - 500 ( +3) = 58
58 (+3) = 61
Timed Quiz
• Beginning with the next slide you will have 30
seconds to answer each question using the mental
math strategy just practiced.
• There will be 10 questions to do.
• Put the title “Mental Math” at the top of your page,
your name to the right, and then numbers 1 to 10
below. Only your answer will go beside the question
number. Your page should look like the following:
Mental Math
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
NOW…. Get ready to begin….
Susan Black
Question 1
480
- 299
Question 2
638
+ 398
Question 3
690
- 502
Question 4
377
+ 504
Question 5
274
- 197
Question 6
498
+ 341
Question 7
430
- 198
Question 8
618
+ 399
Question 9
866
- 303
Question 10
515
+ 299
Now get ready to check your
answers…
1. 181
2. 1036
3. 188
4. 881
5. 77
6. 839
7. 232
8. 1017
9. 563
10. 814