SOLUTION: S30=5235 and A1=15 Find A30 and d

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Question 1071095: S30=5235 and A1=15
Find A30 and d
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
S%5Bn%5D=%28a%5B1%5D%2Ba%5Bn%5D%29%2An%2F2
is my favorite way of calculating the sum.
Substituting,
5235=%2815%2Ba%5B30%5D%29%2A30%2F2
10470=%2815%2Ba%5B30%5D%29%2A30
349=15%2Ba%5B30%5D
349-15=a%5B30%5D
highlight%28a%5B30%5D=334%29
The formula for a%5Bn%5D
based on a%5B1%5D and d is
a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad
so, substituting we get
334=15%2B%2830-1%29d
334=15%2B29d
334-15=29d
319=29d
319%2F29=d
highlight%28d=11%29