Solution:

11

Solution:

12 pentagons

Solution:

51

For Explanation, Watch the video.

Solution:

66

Explanation:
Each arm has 15 blocks and there are four arms ,
The center has 6 blocks.
Total : 15*4 + 6 = 66

Solution:

35

Explanation
4 : 1/2 X 1/2 matchsticks squares
17: 1X1 matchsticks squares
9 : 2X2 matchsticks squares
4 : 3X3 matchsticks squares
1 : 4X4 matchsticks squares
================
35

Solution:

11

Solution:

There are 24 squares in this picture.

Solution:

We colored the squares in the center. They are a total of 6. If you count the ones outside it, you will find 12 squares.

6 + 12 = 18.

Therefore, there are a total of 18 squares.

Solution:

17

Explanation:
Let us begin with the small square. Let us assume that their size is 1 inch.

Now, number of 1 inched squares = 12 (make sure that you don't count the 4 squares in middle twice.)
Number of 2 inched squares (double size) = 5.

Therefore, total squares = 12 + 5 = 17.

Solution:

16 (5 + 1 + 1 + 4 + 5)

black coloured squares : 5
red coloured square : 1
blue coloured square : 1
small green coloured squares in middle : 4
large green coloured squares : 5