SOLUTION: What number is X in this series: 101, 103, X, 115, 131?

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Question 1182258: What number is X in this series: 101, 103, X, 115, 131?
Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!
101, 103, X, 115, 131

Form the first differences and simplify:

103-101, X-103, 115-X, 131-115

2, X-103, 115-X, 16

Since the first and last are first and fourth powers of 2, the most likely
sequence is 

2, 4, 8, 16

Let's see if that works for the first differences.  If so, then this would
need to be a consistent though dependent system:



They both simplify to the same equation

X = 107

That's the most likely solution for X

Checking:

101, 103, 107, 115, 131

Edwin
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