SOLUTION: The first term of an A.P is -2. If the ratio of 5th and 7th is 5:8, what is the common difference?

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Question 1125757: The first term of an A.P is -2. If the ratio of 5th and 7th is 5:8, what is the common difference?
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
term number 5, -2%2B%285-1%29d=-2%2B4d

term 7, -2%2B6d


Ratio of terms
%28-2%2B4d%29%2F%28-2%2B6d%29=5%2F8
%282d-1%29%2F%283d-1%29=5%2F8
5%283d-1%29=8%282d-1%29
15d-5=16d-8
8-5=d
highlight%28d=3%29