SOLUTION: The sum of the first twelve terms of an Arithmetic progression is 168. If the third term is 7, calculate: (I) The common difference (ii) The first term

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Question 1189354: The sum of the first twelve terms of an Arithmetic progression is 168. If the third term is 7, calculate:
(I) The common difference
(ii) The first term
Answer by josgarithmetic(39621) About Me  (Show Source):
You can put this solution on YOUR website!
%2812%2F2%29%28A%2BA%2Bd%28n-1%29%29=168

6%282A%2Bnd-d%29=168

6%282A%2B12d-d%29=168

highlight_green%286%282A%2B11d%29=168%29

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highlight_green%28A%2B2d=7%29

The two outlined equations are linear in two unknown variables. Solve.