Numbers Puzzles

17. Which number is missing from the empty segment?
  What is the next number?
Answer
10
In each circle the top right number equals the average of the left hand numbers and the lower right equals the difference between these numbers.
18. Which number finishes the sequence?
  What is the next number?
Answer
168
Subtract 4 then multiply each number by 3 to give the next number.
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