Class 10

Math

All topics

Sequences and Series

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

- $−35$
- $−50$
- $−55$
- $−65$

$a=−9$

$d=(−14)−(−9)=−5$

$t_{30}=(−9)+(30−1)(−5)=−154$

$t_{20}=(−9)+(20−1)(−5)=−104$

$∴t_{30}−t_{20}=(−154)−(−104)=−50$ (Ans $→$ B)