Find the missing numbers in these proportion problems on a math worksheet.

Let's solve each proportion step by step. In a proportion, the cross products are equal. That is:

If $ a : b = c : d $, then $ a \times d = b \times c $

We'll use this rule to find the missing number in each proportion.

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1. 1 : 3 = 3 : □

Cross multiply:
$ 1 \times \square = 3 \times 3 $
$ \square = 9 $

✔ Answer: 9

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2. 10 : 25 = 20 : □

$ 10 \times \square = 25 \times 20 $
$ 10 \times \square = 500 $
$ \square = 50 $

✔ Answer: 50

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3. 10 : 20 = □ : 30

$ 10 \times 30 = 20 \times \square $
$ 300 = 20 \times \square $
$ \square = 15 $

✔ Answer: 15

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4. 9 : 36 = □ : 32

$ 9 \times 32 = 36 \times \square $
$ 288 = 36 \times \square $
$ \square = 8 $

✔ Answer: 8

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5. 6 : □ = 12 : 20

$ 6 \times 20 = \square \times 12 $
$ 120 = 12 \times \square $
$ \square = 10 $

✔ Answer: 10

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6. 30 : 6 = 15 : □

$ 30 \times \square = 6 \times 15 $
$ 30 \times \square = 90 $
$ \square = 3 $

✔ Answer: 3

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7. 15 : 30 = □ : 40

$ 15 \times 40 = 30 \times \square $
$ 600 = 30 \times \square $
$ \square = 20 $

✔ Answer: 20

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8. 16 : □ = 12 : 24

$ 16 \times 24 = \square \times 12 $
$ 384 = 12 \times \square $
$ \square = 32 $

✔ Answer: 32

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9. 1 : 9 = 5 : □

$ 1 \times \square = 9 \times 5 $
$ \square = 45 $

✔ Answer: 45

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10. 25 : 75 = 18 : □

$ 25 \times \square = 75 \times 18 $
$ 25 \times \square = 1350 $
$ \square = 54 $

✔ Answer: 54

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11. 30 : □ = 60 : 10

$ 30 \times 10 = \square \times 60 $
$ 300 = 60 \times \square $
$ \square = 5 $

✔ Answer: 5

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12. 17 : 34 = □ : 16

$ 17 \times 16 = 34 \times \square $
$ 272 = 34 \times \square $
$ \square = 8 $

✔ Answer: 8

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13. 13 : □ = 12 : 36

$ 13 \times 36 = \square \times 12 $
$ 468 = 12 \times \square $
$ \square = 39 $

✔ Answer: 39

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14. 11 : 88 = 8 : □

$ 11 \times \square = 88 \times 8 $
$ 11 \times \square = 704 $
$ \square = 64 $

✔ Answer: 64

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15. 15 : □ = 11 : 55

$ 15 \times 55 = \square \times 11 $
$ 825 = 11 \times \square $
$ \square = 75 $

✔ Answer: 75

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16. 18 : □ = 1 : 5

$ 18 \times 5 = \square \times 1 $
$ 90 = \square $

✔ Answer: 90

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17. 15 : 45 = 12 : □

$ 15 \times \square = 45 \times 12 $
$ 15 \times \square = 540 $
$ \square = 36 $

✔ Answer: 36

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18. 12 : 60 = 10 : □

$ 12 \times \square = 60 \times 10 $
$ 12 \times \square = 600 $
$ \square = 50 $

✔ Answer: 50

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19. 10 : 50 = □ : 35

$ 10 \times 35 = 50 \times \square $
$ 350 = 50 \times \square $
$ \square = 7 $

✔ Answer: 7

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20. 100 : 250 = □ : 50

$ 100 \times 50 = 250 \times \square $
$ 5000 = 250 \times \square $
$ \square = 20 $

✔ Answer: 20

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✔ Final Answers (in order):

1. 9
2. 50
3. 15
4. 8
5. 10
6. 3
7. 20
8. 32
9. 45
10. 54
11. 5
12. 8
13. 39
14. 64
15. 75
16. 90
17. 36
18. 50
19. 7
20. 20

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You can now fill these into the blanks on the worksheet! Let me know if you'd like it formatted as a completed PDF or printable version.