SOLUTION: The first term of an AP is 7, the last term is 77,the sum is 380. Find the common difference in the series?

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Question 860047: The first term of an AP is 7, the last term is 77,the sum is 380. Find the common difference in the series?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
380 = ½(7 + 77)n
380 = ½(84)n
380 = 42n
190=21n
N is not a whole number.