Question

how do you find the sum of a list of numbers.... ex.... 8,16,....312,320

Answer 1

I know you have to find the average and multiply with the count or somthing like that

Answer 2

This is an ARITHMETIC series: It goes up by a constant number.

To sum this, first figure out how many terms there are in the series.
Let the terms be denoted as such:
T1 = 8
T2 = 16
...
Tn = 8n.

So if Tn = 320 = 8n
then n = 40.
Therefore you have 40 terms.

Now to sum the series you multiply the number of terms by the average of the first and last terms. Then divide by 2.

\[\frac{40(8+320)}2=6560\]

Answer 3

I can explain why this works if you like