Solution:

To make things easier, let us just denote each box with the help of R number and C number i.e. the row number and the column number.

The rule that has been used here is:
R4C1 = (R1C1 * R3C1) - R2C1 = (5 * 2) - 8 = 2
R4C2 = (R1C2 * R3C2) - R2C2 = (7 * 4) - 10 = 18
R4C3 = (R1C3 * R3C3) - R2C3 = (6 * 5) - 12 = 18

Using the same rule for the last box:
R4C4 = (R1C4 * R3C4) - R2C4 = (4 * 9) - 17 = 19

Thus 19 is the missing number.

Solution:

The number will be 30.

In the first circle
(5 + 4) * 2 = 18

In the third circle
2. (12 + 8) * 3 = 60

In the fourth circle
3. (3 + 9) * 4 = 48

Similarly In the fifth circle
4. (4 + 2) * 5 = 30

Solution:

125

Explanation:
The trick that has been used here is that all the corner digits have been reversed and then added. The sum is than placed in the center.

In the first square:
13 + 32 + 11 + 34 = 90

In the second square:
21 + 19 + 27 + 16 = 83

In the third square:
33 + 33 + 22 + 26 = 125

Thus the missing number is 125

Solution:

The solution is given in the attached image.

Solution:

There is no mention if you can use sign or not and thus the only possible way to get this is as follows:

(15 - 9) + (13 - 7) + (7 - 1) + (9 - 1) + (13 - 9)

If you solve inside the brackets, you will get the following equation
6 + 6 + 6 + 8 + 4
Adding all these numbers, you will get 30 which is the required sum.

Solution:

3

Explanation:
Number in the series = (Top Left Number * Bottom Left Number)/(Top Right Number * Bottom Right Number)
= (30 * 2) / (4*5)
= 3

Solution:

If you look closely, you will find a sequence in every alternating number.
192, 222 and 252 form one series where 30 is added each time.
021, 324 and 627 form one series where 303 is added each time.

Thus the next two numbers will be 282 and 930.

Solution:

60

Explanation:
1 + 5 = 12
But it can be true only if we multiply both digits with 2 and then add:
1*2 + 5*2 = 12

2 + 10 = 24
But it can be true only if we multiply both digits with 2 and then add:
2*2 + 10*2 = 24

3 + 15 = 36
But it can be true only if we multiply both digits with 2 and then add:
3*2 + 15*2 = 36

Similarly,
5 + 25 can be true only if we multiply both digits with 2 and then add:
=> 5*2 + 25*2 = 60

Therefore, the missing number is 60.

Solution:

The last missing throw will have 3 as the result. This is because, with each pair of the throws you can find that the total sum is increasing by three and then decreasing by one. Therefore the missing throw be 3.

Solution:

180

2 + 2 = 4 {2 * 2 * 1}
3 + 3 = 18 {3 * 3 * 2}
4 + 4 = 48 {4 * 4 * 3}
6 + 6 = 180 {6 * 6 * 5}