Question

In an AP, if $d=-4$, $n=7$, $a_n=4$, then$a$ is

• A. $6$
• B. $7$
• C. $20$
• D. $28$

Answer 1

The correct option is D

$28$

Find the$a$ of given AP

Given: In an AP, $d=-4$, $n=7$ and $a_n=4$

We know that the $nth$ term of an AP is calculated by using the formula, $a_n=a+\left(n-1\right)d$. where, $a$ is first term,$a_n$ is $nth$ term and , $d$ is the common difference.

On substituting the given values in the above formula. we get,

$$\begin{gathered} \Rightarrow 4=a+(7-1)\times \left(-4\right) \\ \Rightarrow 4=a-24 \\ \Rightarrow a=28 \end{gathered}$$

Hence, $a=28$, so, the correct answer is option (D).