Q23 of 38 Page 5

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

Given: AP - 11, - 8, - 5, …., 49.


To find: 4th term from the end.


Formula Used:


nth term of an AP is:


an = a + (n - 1) d


Where an is the last term.


n = no of terms


a = first term


d = common difference


Explanation:


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


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