What should come in place of question mark (?) in the following number series?

$8 6 ? 23 87 429$

What should come in place of question mark(?)  in the following number series :
$888 888 444 148 ? 7.4$

What should come in place of the question mark (?) in the following number series?
$130 258 514 ? 2050 4098$

What should come in place of the equation mark (?) in the following number series?

$8 6 ? 23 87 429$

Find the wrong number in the following number series:

$5, 65, 715, 6435, 45046, 225225$

What value will come in place of question mark (?) in the number series given below?

$8 15 29 57 113 ?$

What value will come in place of question mark ($?$) in the number series given below?

$5, 7.5, 15, 37.5, ?$

What value will come in place of the question mark $(?)$ in the number series given below?

$558 585 639 720 828 ?$