Answer :

Let the first term, common difference and the number of terms of an AP are a, d and n respectively.


Given that, first term, a = - 5


last term, an = 45


Sum of the terms of the AP , Sn = 120


We know that, if last term of an AP is known, then sum of n terms of an AP is,




240 = 40n


n = 6


Also we know the nth term formula


an = a + (n - 1)d


45 = - 5 + (6 - 1)d


50 = 5d


d = 10


Hence, number of terms and the common difference of an AP are 6 and 10 respectively.



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