Question

The seventh term of an $A.P$ is $30$ and the tenth term is $21$, find the fourth term.

Answer 1

Solution : Let d be common difference

$a_7=30a_{10}=21$

$a_7+3d=a_{10}$

$30+3d=21$

$d=-3$

$a_4=a_7-3d$

$=a_7-3(-3)=30+9$

$\therefore a_4=39$