Solution:

17

Explanation :
The relationship holds for below formula :
pow(x,3) - pow(x,2) - 1
=> 9*9*9 - 9*9 - 1
=> 729 - 81 - 1
=> 647

Similarly,
17*17*17 - 17*17 - 1
=> 4913 - 289 - 1
=> 4623

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 missing letter on the first row is H and the missing letter on the third row is L. Beginning from the top right corner, when you begin clockwise, you will have the word Avalanche.

Solution:

22

Its is sequence of prime numbers and adding 5 to theb number

As we know, 1st seven Prime numbers are :
2 , 3 , 5 , 7 , 11 , 13 , 17

Adding 5 to each number =>
7 , 8 , 10 , 12 , 16 , 18 , 22(Ans)

Solution:

29

Explanation:
If you look closely, you will find that the center number can be obtained by multiplying the largest numbers on the corners and subtracting the smallest number from it.

26 = 7 * 5 – 3^2

In the same manner, every other figure follows. Thus the missing number:
9 * 5 – 4^2
= 45 – 16
= 29

Solution:

186

Explanation :
21+11*1 => 32
32+11*2 => 54
54+11*3 => 87
87+11*4 => 131
131+11*5 => 186

Solution:

61

Reversed digits of squares of number in descending order.

Solution:

4

No Of circles in the number.

Solution:

Each word rhymes with its numeric position in the list. (e.g. 'gun' rhymes with 'one', etc.)

Solution:

31

Each term in the sequence seems to be doubling and then adding 1 to get the next term:
3 * 2 + 1 = 7
7 * 2 + 1 = 15

Following this pattern:
15 * 2 + 1 = 31 .. the missing number

The last number
31 * 2 + 1 = 63