I don't understand the following equation and answer from the MGMAT flash cards. Can someone elaborate for me?
Sn = Sn-1-10 and S3 = 0
Thanks.
Sn = Sn-1-10 and S3 = 0
Thanks.
S3 = 0
S4 = S4-1 - 10 = S3 - 10 = -10
S5 = S4 - 10 = -10 -10 = -20
Common difference b/w each term is -10 (d). The question asks for S25. Now we know S5.
S25 = S5 + n * d [n - number of terms b/w S5 and S25]
= -20 + (20 * -10)
= -20 -200 = -220.
