math puzzle number series

Are you smart enough to solve these puzzles?

Take on the challenge with these difficult puzzles. The puzzles consist of number series with a number omitted. It is up to you to guess what the correct number is. If you do not succeed, you can ask for a hint. Make these puzzles for your relaxation or to develop your brain. You will see that you become better and better when you practice more often with this series of puzzles.