Q29 of 46 Page 1

An Arithmetic Progression 5, 12, 19, ….has 50 terms. Find its last term. Hence find the sum of its last 15 terms.

First term, a = 5


Common difference, d = 12 - 5 = 7


Using the nth term formula, i.e. an = a + (n - 1)d


a50 = a + 49d = 5 + 49(7) = 5 + 343 = 348


Sum of last 10 terms = Sum of 50 terms - sum of 35 terms


Let sum of the last term be S


Using sum of first n terms of an AP formula i.e.






S = 25(353) - 35(124) = 4485


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