SOLUTION: The first term of an Arithmetic progression is 3, find the common difference if the sum of the first eight terms is twice the sum of the first five terms

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Question 972099: The first term of an Arithmetic progression is 3, find the common difference if the sum of the first eight terms is twice the sum of the first five terms
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
3=A%5B1%5D and 2%2A%288%2F2%29%283%2BA%5B1%5D%2B%288-1%29d%29=%285%2F2%29%283%2BA%5B1%5D%2B%285-1%29d%29----this is just an exact transcription of the worded description, using formula for sum of arithmetic sequence.

8%283%2B3%2B7d%29=%285%2F2%29%283%2B3%2B4d%29
8%286%2B7d%29=%285%2F2%29%286%2B4d%29
8%2A6%2B8%2A7d=15%2B10d
48%2B46d=15
46d=15-48
46d=-33
highlight%28d=-33%2F46%29

Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!

The first term of an Arithmetic progression is 3, find the common difference if the sum of the first eight terms is twice the sum of the first five terms
Common difference: highlight_green%283%2F4%29