Question

In the following $A.P.$, write the missing term
$.....,13,....,3$

Answer 1

Let the numbers be, $a,a+d,a+2d,a+3d$

$13=a+d$..........(1)

$3=a+3d$.......(2)

(2)-(1) gives,

$2d=-10\Rightarrow d=-5$

From (2)

$3=a+3(-5)$

$\therefore a=18$

The terms of the series are,

$18,13,8,3$