Question

The first term of an A.P. is $5,$ the common difference is $3$ and the last term is $80,$ find the number of terms.

• A. $25$
• B. $26$
• C. $24$
• D. $27$

Answer 1

The correct option is B $26$

Clearly, the given sequence is an AP with first term $a=5$ and common difference $d=3$.
Let there are $n$ terms in this AP. Therefore,
$a_n=80\Rightarrow a+(n-1)d=80$
$\Rightarrow 5+(n-1)3=80$
$\Rightarrow (n-1)3=75$
$\Rightarrow n-1=25$
$\Rightarrow n=26$
Hence, there are $26$ terms in given AP