How can I calculate the sum of summed numbers?

the sum of 2 + 4 + 6 = 4





but how can I sum 2 + 4 = 3


then sum 3 + 6 = 4.5





Is there a formula for this?How can I calculate the sum of summed numbers?
OK it's not difficult to follow the pattern.





You sum the number the normal way. Then divide by the number of terms on the left hand side.





x1 + x2 + ... + xn = (x1 + x2 + ... + xn) / nHow can I calculate the sum of summed numbers?
You are creating a new system of addition. You need to come up with a consistent system that gives the answers that you want.





I would have thought that the easy solution would be sum the numbers using the old style math and then divide by 2. This works for the last two equations, however the first one should be 6 not 4 if that is the case.