mental math subtracting tens and compensate strategy: when subtracting numbers ending in 7, 8, or 9,...
TRANSCRIPT
MENTAL MATH
Subtracting Tens and Compensate
Strategy: When subtracting numbers ending in 7, 8, or 9, round that number to the nearest tens and then add on 3, 2, or 1 to the answer.
Example: 75 – 57 75 – 60 = 15 + 3 = 18
Practice with….
Subtracting using Tens…
64- 38
64 – 40 = 24 +2 = 26
49- 28
49 – 30 = 19 + 2 = 21
91- 57
91 – 60 = 31 + 3 = 34
74- 49
74 – 50 = 24 + 1 = 25
65- 39
65 – 40 = 25 + 1 = 26
Timed Quiz
• Beginning with the next slide you will have 10 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 Susan Black
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
NOW…. Get ready to begin….
Question 1
48 - 27
Question 2
74 - 38
Question 3
65 - 49
Question 4
83 - 59
Question 5
25 - 17
Question 6
85 - 38
Question 7
43 - 19
Question 8
71 - 37
Question 9
94 - 38
Question 10
54 - 29
Now get ready to check your answers…
1. 212. 363. 164. 245. 86. 477. 248. 349. 5610. 25