The 4th term from the end of an AP - 11, - 8, - 5, …., 49 is


First term, a = - 11


Common difference, a2 -a = - 8 - (- 11) = 3


Let the last term be an


an = a + (n - 1)d


49 = - 11 + (n - 1)3


49 + 11 = (n - 1)3


n - 1 = 60/3


n - 1 = 20


n = 21


4th term from last will be 18th term from starting


And a18 = a + 17d


= - 11 + 17(3)


= 40


Alternatively we can use the direct formula


an = l - (n - 1)d


where, an = nth term from last of an AP


l = last term


d = common difference

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