The first term of an A.P. is 5,
Question:

The first term of an A.P. is 5, the common difference is 3 and the last term is 80;

Solution:

In the given problem, we are given an A.P whose,

First term (a) = 5

Last term $\left(a_{e}\right)=80$

Common difference (d) = 3

We need to find the number of terms present in it (n)

So here we will find the value of $n$ using the formula, $a_{n}=a+(n-1) d$

So, substituting the values in the above mentioned formula

$80=5+(n-1) 3$

$80-5=3 n-3$

$75+3=3 n$

$n=\frac{78}{3}$

$n=26$

Thus, $n=26$

Therefore, the number of terms present in the given A.P is 26