Question

Find S25 for -7+ -2 + 3 + 8 +…

I got -2275 following but I don't think that's right. Any advice would be awesome! Thanks.

Answer 1

How'd you get that?

Answer 2

Wouldn't it just be 113?

Answer 3

so we know that a1 = -7
tell me what is d ?
d = a2 - a1

Answer 4

when you find d you can find a25:
a25 = a1 + (25-1)*d = a1 + 24d

Answer 5

after you find a25
you can find S25 :
S25 = 25 * (a1 + a25) / 2

Answer 6

@Coolsector : Your answer is right !:)
:D
@maddie.jones47563 : Flow the Coolsector s answer !

Answer 7

Okay. Thanks you guys :) @pathosdebater @E.ali @Coolsector