Question:

If 18, a, (b − 3) are in AP, then find the value of (2− b).

Solution:

It given that 18, a, (b − 3) are in AP.

$\therefore a-18=(b-3)-a$

$\Rightarrow a+a-b=18-3$

$\Rightarrow 2 a-b=15$

Hence, the required value is 15