Printable primary math worksheet for math grades 1 to 6 based on ... - Free Printable

Let's solve each proportion step by step. A proportion is an equation stating that two ratios are equal. We can solve for the missing number using cross-multiplication:

If
$$
a : b = c : d
$$
then
$$
a \cdot d = b \cdot c
$$

We'll go through each problem one by one.

---

1. $ 120 : 80 = 90 : \boxed{?} $

Cross-multiply:
$ 120 \cdot ? = 80 \cdot 90 $
$ 120x = 7200 $
$ x = \frac{7200}{120} = 60 $

✔ Answer: 60

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2. $ 20 : 15 = 40 : \boxed{?} $

$ 20 \cdot ? = 15 \cdot 40 $
$ 20x = 600 $
$ x = 30 $

✔ Answer: 30

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3. $ 150 : 300 = \boxed{?} : 120 $

$ 150 \cdot 120 = 300 \cdot x $
$ 18000 = 300x $
$ x = \frac{18000}{300} = 60 $

✔ Answer: 60

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4. $ 196 : 182 = \boxed{?} : 130 $

$ 196 \cdot 130 = 182 \cdot x $
$ 25480 = 182x $
$ x = \frac{25480}{182} = 140 $

✔ Answer: 140

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5. $ 25 : \boxed{?} = 75 : 12 $

$ 25 \cdot 12 = ? \cdot 75 $
$ 300 = 75x $
$ x = \frac{300}{75} = 4 $

✔ Answer: 4

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6. $ 15 : 90 = 13 : \boxed{?} $

$ 15 \cdot ? = 90 \cdot 13 $
$ 15x = 1170 $
$ x = \frac{1170}{15} = 78 $

✔ Answer: 78

---

7. $ 12 : 125 = \boxed{?} : 250 $

$ 12 \cdot 250 = 125 \cdot x $
$ 3000 = 125x $
$ x = \frac{3000}{125} = 24 $

✔ Answer: 24

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8. $ 45 : \boxed{?} = 18 : 40 $

$ 45 \cdot 40 = ? \cdot 18 $
$ 1800 = 18x $
$ x = \frac{1800}{18} = 100 $

✔ Answer: 100

---

9. $ 45 : 80 = 90 : \boxed{?} $

$ 45 \cdot ? = 80 \cdot 90 $
$ 45x = 7200 $
$ x = \frac{7200}{45} = 160 $

✔ Answer: 160

---

10. $ 24 : 100 = 60 : \boxed{?} $

$ 24 \cdot ? = 100 \cdot 60 $
$ 24x = 6000 $
$ x = \frac{6000}{24} = 250 $

✔ Answer: 250

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11. $ 20 : \boxed{?} = 70 : 63 $

$ 20 \cdot 63 = ? \cdot 70 $
$ 1260 = 70x $
$ x = \frac{1260}{70} = 18 $

✔ Answer: 18

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12. $ 150 : 750 = \boxed{?} : 35 $

$ 150 \cdot 35 = 750 \cdot x $
$ 5250 = 750x $
$ x = \frac{5250}{750} = 7 $

✔ Answer: 7

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13. $ 15 : \boxed{?} = 45 : 285 $

$ 15 \cdot 285 = ? \cdot 45 $
$ 4275 = 45x $
$ x = \frac{4275}{45} = 95 $

✔ Answer: 95

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14. $ 25 : 80 = 5 : \boxed{?} $

$ 25 \cdot ? = 80 \cdot 5 $
$ 25x = 400 $
$ x = \frac{400}{25} = 16 $

✔ Answer: 16

---

15. $ 120 : \boxed{?} = 60 : 175 $

$ 120 \cdot 175 = ? \cdot 60 $
$ 21000 = 60x $
$ x = \frac{21000}{60} = 350 $

✔ Answer: 350

---

16. $ 160 : \boxed{?} = 128 : 144 $

$ 160 \cdot 144 = ? \cdot 128 $
$ 23040 = 128x $
$ x = \frac{23040}{128} = 180 $

✔ Answer: 180

---

17. $ 144 : 180 = 12 : \boxed{?} $

$ 144 \cdot ? = 180 \cdot 12 $
$ 144x = 2160 $
$ x = \frac{2160}{144} = 15 $

✔ Answer: 15

---

18. $ 35 : 55 = 70 : \boxed{?} $

$ 35 \cdot ? = 55 \cdot 70 $
$ 35x = 3850 $
$ x = \frac{3850}{35} = 110 $

✔ Answer: 110

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19. $ 380 : 100 = \boxed{?} : 75 $

$ 380 \cdot 75 = 100 \cdot x $
$ 28500 = 100x $
$ x = \frac{28500}{100} = 285 $

✔ Answer: 285

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20. $ 240 : 360 = \boxed{?} : 120 $

$ 240 \cdot 120 = 360 \cdot x $
$ 28800 = 360x $
$ x = \frac{28800}{360} = 80 $

✔ Answer: 80

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✔ Final Answers (in order):

1. 60
2. 30
3. 60
4. 140
5. 4
6. 78
7. 24
8. 100
9. 160
10. 250
11. 18
12. 7
13. 95
14. 16
15. 350
16. 180
17. 15
18. 110
19. 285
20. 80

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You can now fill in the blanks on the worksheet with these answers.

Let me know if you'd like a printable version or explanation of any specific problem!