Question

What is the sum of a 56-term arithmetic sequence where the first term is 6 and the last term is 391?

Answer 1

\[a_n=a_o+d(n-1)\]
might be a good start

Answer 2

nah, we just need first and last terns dont we

Answer 3

56(6+391)
---------- sounds better
2

Answer 4

6 6+d 6+2d ... 391
391 391-d 391-2d ... 6
-------------------------
6+391 ....... 56 times

but we dont want 2 sets worth so we divide the results in half