Missing Number Puzzles Questions

7. Which number should replace the question mark?
  What is the next number?
Answer
Ans = 1.
Take the difference in the pairs of numbers right and left to obtain the numbers top and bottom. So, difference between 8 and 5 is 3 and difference between 7 and 1 is 6.
8. What number should replace the question mark?
  What is the next number?
Answer
Ans = 51.
9 x 5 = 45 + 6 = 51.
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