Question

In the arithmetic progression given below, find the common difference.
1, a, b, c, 9

• A. 0
• B. 3
• C. 1
• D. 2

Answer 1

The correct option is D

2

There are five terms in this AP
$a_n$ = $a_1$ + (n - 1)d
$\Rightarrow$ $a_n-a_1=(n-1)d$
$\Rightarrow$ $\frac{a_n-a_1}{n-1}=d$

Here, $a_1=1;n=5;a_n=9$
Therefore the common difference,
$d=\frac{9-1}{5-1}=2$