Question 1198565
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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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<pre>
Using the formula for the sum of an arithmetic progression, we have

    {{{((a[1]+a[n])/2)*n}}} = 380,

or

    {{{((7+77)/2)*n}}} = 380

    {{{(84/2)*n}}} = 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.
</pre>

Solved (i.e. disproved).


My condolences.