Question

the first term of an ap is 5, common difference is 3 and the last term is 80. Find the number of terms

Answer 1

a= 5
d = 3
a of n = 80
according to question :-

80= a+(n-1)d

80 = 5 + (n-1)3
80= 5+3n-3
80=2+ 3n
78 = 3n
n = 78/3
    = 26

therefore number of terms is 26

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Answer 2

Hi ,

Let a and d are first term and

common difference of an AP.

a = 5 ;

d = 3 ;

Let number of terms = n

last term = l = 80

a + ( n - 1 )d = 80

5 + ( n - 1 ) 3 = 80

( n - 1 ) 3 = 80 - 5

( n - 1 ) 3 = 75

n - 1 = 75/3

n - 1 = 25

n = 25 + 1

n = 26

Therefore ,

26 th term of given AP is 80.

I hope this helps you.

:)