MENTAL MATH Subtracting Tens and Compensate Strategy: When subtracting numbers ending in 7, 8, or 9,...

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MENTAL MATH

Transcript of MENTAL MATH Subtracting Tens and Compensate Strategy: When subtracting numbers ending in 7, 8, or 9,...

Page 1: 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.

MENTAL MATH

Page 2: 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.

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

Page 3: 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.

Practice with….

Subtracting using Tens…

Page 4: 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.

64- 38

64 – 40 = 24 +2 = 26

Page 5: 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.

49- 28

49 – 30 = 19 + 2 = 21

Page 6: 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.

91- 57

91 – 60 = 31 + 3 = 34

Page 7: 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.

74- 49

74 – 50 = 24 + 1 = 25

Page 8: 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.

65- 39

65 – 40 = 25 + 1 = 26

Page 9: 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.

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:

Page 10: 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.

Mental Math Susan Black

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NOW…. Get ready to begin….

Page 11: 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.

Question 1

48 - 27

Page 12: 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.

Question 2

74 - 38

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Question 3

65 - 49

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Question 4

83 - 59

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Question 5

25 - 17

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Question 6

85 - 38

Page 17: 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.

Question 7

43 - 19

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Question 8

71 - 37

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Question 9

94 - 38

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Question 10

54 - 29

Page 21: 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.

Now get ready to check your answers…

1. 212. 363. 164. 245. 86. 477. 248. 349. 5610. 25