Solution:

As shown below, we can make equation as 6 = 6 = 6.

Solution:

Puzzle solved as shown in pic below

Solution:

One for all or all for one.

Solution:

Both will rotate at Same speed.

Explanation:
Gears of the same size will always rotate at constant speeds despite any smaller or larger gears in between them.

Solution:

We just added four matchsticks as shown in below picture.

Solution:

Yes, show in below picture

Solution:

in between job

Solution:

Solution is shown below,

Solution:

Ball in your court

Solution:

Explained in picture below