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. To find the missing number, we use cross-multiplication:

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

We'll solve each one and explain.

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1. 120 : 80 = 90 : ?

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

✔ Answer: 60

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2. 20 : 15 = 40 : ?

$$
20 \cdot x = 15 \cdot 40 \\
20x = 600 \\
x = \frac{600}{20} = 30
$$

✔ Answer: 30

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3. 150 : 300 = ? : 120

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

✔ Answer: 60

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4. 196 : 182 = ? : 130

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

✔ Answer: 140

---

5. 25 : ? = 75 : 12

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

✔ Answer: 4

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6. 15 : 90 = 13 : ?

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

✔ Answer: 78

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7. 12 : 125 = ? : 250

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

✔ Answer: 24

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8. 45 : ? = 18 : 40

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

✔ Answer: 100

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9. 45 : 80 = 90 : ?

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

✔ Answer: 160

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10. 24 : 100 = 60 : ?

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

✔ Answer: 250

---

11. 20 : ? = 70 : 63

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

✔ Answer: 18

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12. 150 : 750 = ? : 35

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

✔ Answer: 7

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13. 15 : ? = 45 : 285

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

✔ Answer: 95

---

14. 25 : 80 = 5 : ?

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

✔ Answer: 16

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15. 120 : ? = 60 : 175

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

✔ Answer: 350

---

16. 160 : ? = 128 : 144

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

✔ Answer: 180

---

17. 144 : 180 = 12 : ?

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

✔ Answer: 15

---

18. 35 : 55 = 70 : ?

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

✔ Answer: 110

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19. 380 : 100 = ? : 75

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

✔ Answer: 285

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20. 240 : 360 = ? : 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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Let me know if you'd like this in a printable format or with steps for each!