Question 1134391
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There are 27 equal gaps between the 1-st and the 28-th terms,


while the distance between these terms is  31 - (-5) = 36.



Hence, the common difference (the gap between the neighbor terms) is  {{{-36/27}}} = {{{-1}}}{{{1/3}}}.      <U>ANSWER</U>


<U>CHECK</U>.  {{{a[28]}}} = {{{a[1] + d*(28-1)}}} = 31 - {{{1}}}{{{1/3}}}.{{{27}}} = 31 - {{{(4/3)*27}}} = 31 - 36 = -5.    ! Correct !
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