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

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Question 1198565: The first term of an AP is 7. And the last term is 77.and the sum is 380. Find the common difference in the series.
Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
.
The first term of an AP is 7. And the last term is 77.and the sum is 380.
Find the common difference in the series.
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Using the formula for the sum of an arithmetic progression, we have

    %28%28a%5B1%5D%2Ba%5Bn%5D%29%2F2%29%2An = 380,

or

    %28%287%2B77%29%2F2%29%2An = 380

    %2884%2F2%29%2An = 380

    42n = 380


      n = 380/42 = 9.0476 (rounded).


Since "n" is not a whole number, I conclude that the problem is DEFECTIVE 
and describes a situation which never may happen.

Solved (i.e. disproved).

My condolences.