Question

If 24th term of an ap is twice its 10th term . Show that 72nd term is four times of its 15th term .

Answer 1

$a + 23d = 2(a + 9d)$
$by \: solving$
$a = 5d$
$then \: \: a + 71d = 4(a + 14d)$
$3a = 15d$
$a = 5d$
hence proved....