Answer:

1. N:12 = 15:36

36N = 12 × 15

36N = 180

36N/36 = 180/36

N = 5

2. 6:1 = 1:N

6N = 1 × 1

6N = 1

6N/6 = 1/6

N = 1/6

3. 15/N = 10/30

10N = 15 × 30

10N = 450

10N/10 = 450/10

N = 45

4. 12:N = 6:5

6N = 12 × 5

6N = 60

6N/6 = 60/6

N = 10

5. 16:N = N:1

N² = 16 × 1

N² = 16

√N² = √16

N = 4

6. 2N:4 = 18:30

60N = 4 × 18

60N = 72

60N/60 = 72/60

N = 72/60 ÷ 12/12

N = 6/5

7. 13:11 = 39:N

13N = 11 × 39

13N = 429

13N/13 = 429/13

N = 33

8. N:100 = 3:4

4N = 3 × 100

4N = 300

4N/4 = 300/4

N = 75

9. 4N/70 = 2/7

28N = 70 × 2

28N = 140

28N/28 = 140/28

N = 5

10. N/100 = 3/5

5N = 100 × 3

5N = 300

5N/5 = 300/5

N = 60