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