Answer :

Given,


a = 5, last term, l = an = 80


Common difference, d = 3


We know, an = a + (n – 1)d where a is first term or a1 and d is common difference and n is any natural number


an = 5 + (n – 1)3


an = 5 + 3n – 3


an = 3n + 2


To find total terms of the A.P., put an = 80 as 80 is last term of A.P.


3n + 2 = 80


3n = 80 – 2


3n = 78



n = 26


Hence, there are total 26 terms in the given A.P.


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