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In the first problem, I used 2, 3 and 5 as an example. I found that it's always double the third number. This is because if you already know the sum of the first two (the first two add to the third) then all you need to do is double. This is why the sum is double the third number.

In the second problem, I used 2, 3, 5 and 8. It equaled the third number. The first and second numbers and closer than the third and fourth. The fourth number minus the third always equals the second number, meaning that the difference between the third and fourth numbers is the same as the first and third. The mean average was found and it always finds the middle number. This is the reason behind this problem.