Question

Find the sum of the given arithmetic series.

24 + 48 + 72 + 96 + ... + 480

Answer 1

Do you remember what the formula is?

Answer 2

Well my class is based on pretests and usually I forget what I do once i pass each test..but i have a_n=a_1+(n-1)d and for the sum S_n=n(a_1+a_n)/2

Answer 3

Yeah so just start with finding n, using the first expression you gave me

Answer 4

Then sub that value of n into the second equation c:

Answer 5

Okay thanks :)

Answer 6

Hope this helped c:

Answer 7

Oh sorry had a derp moment..
Remember how a_n can be (a_4) - (a_3) = (a_2)
Or (a_3) - (a_2) = (a_1)
You can use it to help find n