LESSON Practice B Variables and Expressions



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Date

Class

LESSON Practice B 2-1 Variables and Expressions

Evaluate each expression to find the missing values in the tables.

1.

n

n8

2.

n

25 n

7

15

20

5

9

5

22

18

35

9

3.

n

8

9

11

12

n?7 56

4.

n

2

6

4

8

24 n 12

Find an expression for each table.

5.

n

35

50

5

20

20

35

85

100

7. A car is traveling at a speed of 55 miles per hour. You want to write an algebraic expression to show how far the car will travel in a certain number of hours. What will be your constant? your variable?

6.

n

13

26

9

18

30

60

25

50

8. Shawn evaluated the algebraic expression x 4 for x 12 and gave an answer of 8. What was his error? What is the correct answer?

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

10

Holt Middle School Math Course 1

LESSON Practice B 2-1 Variables and Expressions

Evaluate each expression to find the missing values in the tables.

1.

n

n8

2.

n

25 n

7

15

9

17

22

30

35

43

20

5

5

20

18

7

9

16

3.

n

8

9

11

12

n?7

56

63 77 84

4.

n

2

6

4

8

24 n

12

4 6 3

Find an expression for each table.

5.

n

n 15

35

50

5

20

20

35

85

100

7. A car is traveling at a speed of 55 miles per hour. You want to write an algebraic expression to show how far the car will travel in a certain number of hours. What will be your constant? your variable?

55 will be the constant, and the

number of hours will be the

variable.

6.

n

13

9

30

25

n?2

26 18 60 50

8. Shawn evaluated the algebraic expression x 4 for x 12 and gave an answer of 8. What was his error? What is the correct answer?

He used subtraction instead of division. The correct answer is 3.

LESSON Practice C 2-1 Variables and Expressions

Evaluate each expression to find the missing values in the tables.

1.

n

n 15

2.

n

3n 9

30

2

3

0

75

5

8

15

15

1

10

21

105

7

29

78

Find an expression for each table.

3.

n

n 17

34

51

55

72

26

43

100

117

4.

n

11

9

2

75

n ? 12

132 108 24 900

Evaluate each expression for the given value of the variable.

5. 5x 2 for x 4

6. 63 8z for z 7

7. 176 p for p 2

22

8. 6v4 11 for v 4

5

11. 48 n for n 3

7

9. 19w for w 5

95

12. x x x for x 15

88

10. 98 5q for q 7

63

13. 16 n 2 for n 3

16

45

14. What is the next expression in the following pattern: 4n; 8n; 16n?

32n

25

15. What is the next expression in the pattern x 27; x 24; x 21?

x 18

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

10

Holt Middle School Math Course 1

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

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Holt Middle School Math Course 1

LESSON Reteach 2-1 Variables and Expressions

A variable is a letter or a symbol that stands for a number that can change. A constant is an amount that does not change.

A mathematical phrase that contains at least one variable is an algebraic expression. In the algebraic expression x 5, x is a variable and 5 is a constant.

When you evaluate an algebraic expression, substitute a number for the variable and then find the value.

LESSON Challenge 2-1 Express Trains

Use the expression written on the side of each train's engine to

find the missing values for the cars it pulls. Then choose your

own value for the variable to fill in the last caboose on each train.

1.

6

8

4

5

n7

n 42

n 56

n 28

n 35

To evaluate the algebraic expression m 8 for m 12, first replace

2.

the variable m in the expression with 12.

m8

12 8

Then find the value of the expression.

12 8 4

The value of m 8 is 4 when m 12.

3.

Evaluate each expression for the given value of the variable.

1. x 5, for x 6 2. 3p, for p 5

11

15

3. z 4, for z 24 4. w 7, for w 15

6

8

2x 5 c 12

11 x3

4 c 48

21

x8

2

c 24

25

x 10

15 x5

5

c 60

8 c 96

To find an expression for a table of values, look for patterns.

4.

31

11

46

16

x 3 12 4 16 5 20

Think: 3 ? ? 12 Think: 4 ? ? 16 Think: 5 ? ? 20

x(4) is an expression for the table.

3 ? 4 12 4 ? 4 16 5 ? 4 20

5p 9

p8

5.

45

p4

18

p 11

p5

81

27

Find an expression for each table.

5. x

3 10

5 12

6. b 25 5 15 3

7 14

10 2

x7

b5

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

7. g 2 12 6 36 8 48

g6

8. y

97

10 8

14 12

y2

7m 2m

m5

m2

m9

m3

Possible answers are given on each caboose. Accept all answers that correctly match the chosen variable and the train's expression.

12

Holt Middle School Math Course 1

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

13

Holt Middle School Math Course 1

Copyright ? by Holt, Rinehart and Winston. All rights reserved.

82

Holt Middle School Math Course 1

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