Question

If $t_n$ be the $n^{th}$ term of the A.P. $-9,-14,-19,....,$ what is the value of $t_{30}-t_{20}$?

• A. $-35$
• B. $-50$
• C. $-55$
• D. $-65$

Answer 1

The correct option is B $-50$

Given series: $-9,-14,-19,...$

Here $a=-9$

and $d=(-14)-(-9)=-5$

$t_{30}=(-9)+(30-1)(-5)$

$=-154$

$t_{20}=(-9)+(20-1)(-5)$

$=-104$

$\therefore t_{30}-t_{20}=(-154)-(-104)$

$=-50$