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Amy Ferguson Moncure

7th Grade Math · Unit 5

Write and Solve
a Proportion

Solve a proportion by cross-multiplying, then dividing.

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Key Ideas Easy Medium Hard
What to Remember

Two equal ratios

A proportion is two equal ratios.

Cross-multiply

Cross-multiply, then divide.

Level 1

Easy

Whole-number answers

Example
Solve the proportion for x. This finds the missing number.
24 = 3x

24 = 3x

Cross-multiply.

2x = 4 × 3

2x = 12

Divide both sides by 2.

x = 6

Answer: 6

1
Solve the proportion for x. This finds the missing number.
12 = 5x
Show Answer

12 = 5x

Cross-multiply.

1x = 2 × 5

1x = 10

Divide both sides by 1.

x = 10

Answer: 10

2
Solve the proportion for x. This finds the missing number.
26 = 3x
Show Answer

26 = 3x

Cross-multiply.

2x = 6 × 3

2x = 18

Divide both sides by 2.

x = 9

Answer: 9

3
Solve the proportion for x. This finds the missing number.
39 = 4x
Show Answer

39 = 4x

Cross-multiply.

3x = 9 × 4

3x = 36

Divide both sides by 3.

x = 12

Answer: 12

4
Solve the proportion for x. This finds the missing number.
48 = 5x
Show Answer

48 = 5x

Cross-multiply.

4x = 8 × 5

4x = 40

Divide both sides by 4.

x = 10

Answer: 10

5
Solve the proportion for x. This finds the missing number.
23 = 8x
Show Answer

23 = 8x

Cross-multiply.

2x = 3 × 8

2x = 24

Divide both sides by 2.

x = 12

Answer: 12

6
Solve the proportion for x. This finds the missing number.
35 = 6x
Show Answer

35 = 6x

Cross-multiply.

3x = 5 × 6

3x = 30

Divide both sides by 3.

x = 10

Answer: 10

7
Solve the proportion for x. This finds the missing number.
45 = 8x
Show Answer

45 = 8x

Cross-multiply.

4x = 5 × 8

4x = 40

Divide both sides by 4.

x = 10

Answer: 10

8
Solve the proportion for x. This finds the missing number.
14 = 7x
Show Answer

14 = 7x

Cross-multiply.

1x = 4 × 7

1x = 28

Divide both sides by 1.

x = 28

Answer: 28

9
Solve the proportion for x. This finds the missing number.
25 = 6x
Show Answer

25 = 6x

Cross-multiply.

2x = 5 × 6

2x = 30

Divide both sides by 2.

x = 15

Answer: 15

10
Solve the proportion for x. This finds the missing number.
510 = 4x
Show Answer

510 = 4x

Cross-multiply.

5x = 10 × 4

5x = 40

Divide both sides by 5.

x = 8

Answer: 8

Level 2

Medium

A fraction in the proportion

Example
Solve the proportion for x. This finds the missing number.
124 = 3x

124 = 3x

Cross-multiply.

12x = 4 × 3

12x = 12

Divide both sides by 12.

x = 24

Answer: 24

1
Solve the proportion for x. This finds the missing number.
135 = 2x
Show Answer

135 = 2x

Cross-multiply.

13x = 5 × 2

13x = 10

Divide both sides by 13.

x = 30

Answer: 30

2
Solve the proportion for x. This finds the missing number.
143 = 4x
Show Answer

143 = 4x

Cross-multiply.

14x = 3 × 4

14x = 12

Divide both sides by 14.

x = 48

Answer: 48

3
Solve the proportion for x. This finds the missing number.
326 = 5x
Show Answer

326 = 5x

Cross-multiply.

32x = 6 × 5

32x = 30

Divide both sides by 32.

x = 20

Answer: 20

4
Solve the proportion for x. This finds the missing number.
234 = 5x
Show Answer

234 = 5x

Cross-multiply.

23x = 4 × 5

23x = 20

Divide both sides by 23.

x = 30

Answer: 30

5
Solve the proportion for x. This finds the missing number.
349 = 2x
Show Answer

349 = 2x

Cross-multiply.

34x = 9 × 2

34x = 18

Divide both sides by 34.

x = 24

Answer: 24

6
Solve the proportion for x. This finds the missing number.
5210 = 1x
Show Answer

5210 = 1x

Cross-multiply.

52x = 10 × 1

52x = 10

Divide both sides by 52.

x = 4

Answer: 4

7
Solve the proportion for x. This finds the missing number.
129 = 4x
Show Answer

129 = 4x

Cross-multiply.

12x = 9 × 4

12x = 36

Divide both sides by 12.

x = 72

Answer: 72

8
Solve the proportion for x. This finds the missing number.
312 = 3x
Show Answer

312 = 3x

Cross-multiply.

3x = 12 × 3

3x = 32

Divide both sides by 3.

x = 12

Answer: 12

9
Solve the proportion for x. This finds the missing number.
232 = 4x
Show Answer

232 = 4x

Cross-multiply.

2x = 32 × 4

2x = 6

Divide both sides by 2.

x = 3

Answer: 3

10
Solve the proportion for x. This finds the missing number.
13 = 12x
Show Answer

13 = 12x

Cross-multiply.

1x = 3 × 12

1x = 32

Divide both sides by 1.

x = 32

Answer: 32

Level 3

Hard

A real life proportion

Example
Solve the proportion for x. This finds the number of red beads.
25 = 8x

25 = 8x

Cross-multiply.

2x = 5 × 8

2x = 40

Divide both sides by 2.

x = 20

Answer: 20

1
Solve the proportion for x. This finds the actual length.
34 = 9x
Show Answer

34 = 9x

Cross-multiply.

3x = 4 × 9

3x = 36

Divide both sides by 3.

x = 12

Answer: 12

2
Solve the proportion for x. This finds the cost.
52 = 15x
Show Answer

52 = 15x

Cross-multiply.

5x = 2 × 15

5x = 30

Divide both sides by 5.

x = 6

Answer: 6

3
Solve the proportion for x. This finds the number of blue tiles.
410 = 6x
Show Answer

410 = 6x

Cross-multiply.

4x = 10 × 6

4x = 60

Divide both sides by 4.

x = 15

Answer: 15

4
Solve the proportion for x. This finds the number of miles.
68 = 9x
Show Answer

68 = 9x

Cross-multiply.

6x = 8 × 9

6x = 72

Divide both sides by 6.

x = 12

Answer: 12

5
Solve the proportion for x. This finds the number of minutes.
13 = 7x
Show Answer

13 = 7x

Cross-multiply.

1x = 3 × 7

1x = 21

Divide both sides by 1.

x = 21

Answer: 21

6
Solve the proportion for x. This finds the number of students.
27 = 6x
Show Answer

27 = 6x

Cross-multiply.

2x = 7 × 6

2x = 42

Divide both sides by 2.

x = 21

Answer: 21

7
Solve the proportion for x. This finds the weight in ounces.
38 = 6x
Show Answer

38 = 6x

Cross-multiply.

3x = 8 × 6

3x = 48

Divide both sides by 3.

x = 16

Answer: 16

8
Solve the proportion for x. This finds the number of pages.
56 = 10x
Show Answer

56 = 10x

Cross-multiply.

5x = 6 × 10

5x = 60

Divide both sides by 5.

x = 12

Answer: 12

9
Solve the proportion for x. This finds the height in inches.
43 = 12x
Show Answer

43 = 12x

Cross-multiply.

4x = 3 × 12

4x = 36

Divide both sides by 4.

x = 9

Answer: 9

10
Solve the proportion for x. This finds the number of cups.
32 = 5x
Show Answer

32 = 5x

Cross-multiply.

3x = 2 × 5

3x = 10

Divide both sides by 3.

x = 103

Answer: 103

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