Answers

2016-07-03T18:54:37+08:00
Given:
a1 = 3; an = 99; d = 3

an = a1 + (n-1)d
99 = 3 + (n-1)3
99-3 = 3n-3
*eliminate both the negative three
99 = 3n
*divide both by three
n = 33

Sn = n/2 [a1+an]
S33 = 33/2 [1+99]
S33 = 33/2 [100]
S33 = 1650

answer: S33 = 1650
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