Puzzles with number sequences in one line

Puzzles, riddles, brain teasers, conundrums, logic questions in pictures. In these tasks you need to find the number that should stand in place of the question mark. These number riddles, brain teasers and conundrums are designed as a sequence of numbers on one line. To check your answer, click on the «Answer» button located below the task. After this, the correct answer and explanations will appear. Below you can select other questions on this topic. Typically each topic has 20 questions or more. At the same time, the complexity of logical problems gradually increases. First there will be easy questions, then medium, then difficult. Try to complete tasks as quickly as possible.
Question - 5
To complete this logic riddle you need to understand the rule of increasing and decreasing numbers. Perhaps there is some kind of cyclicity here.
Correct answer = 15.
To obtain subsequent numbers, you must alternately add +4, -1.
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