SOLUTION: The first term of an arithmetic progression is -8. The ratio of the 7th term to the 9th term is 5:8. Calculate the common difference.

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Question 918942: The first term of an arithmetic progression is -8. The ratio of the 7th term to the 9th term is 5:8. Calculate the common difference.
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
a%5Bn%5D=-8%2B%28n-1%29d, index being n, common difference being d.

Ratio of seventh term to ninth term is 5:8,
%28-8%2B%287-1%29d%29%2F%28-8%2B%289-1%29d%29=5%2F8
That is the key equation to form; and solving it should be a comfortable process. You basically want to determine the value of d, common difference between terms.