Question

Find the ${20}^{th}$ term from the last term of the $A.P.3,8,\mathrm{13.........253}$.

Answer 1

$a_1=253$

$d=-5$

$\therefore a_{20}=253+19d$

$a_{20}=253-19\left(5\right)$

$a_{20}=253-95$

$a_{20}=158$.