Question

Please help! What is the value of the fourth term in a geometric sequence for which a1 = 30 and r = 1/2?

Answer 1

Without using the formula for the nth term you can find the 4th term easily:
Geometric sequence is formed by multiplying each term by the common ratio r.
1st term = 30
2nd term = 30 * 1/2 = 15
3rd term = 15 * 1/2 = 7.5
4th term = ?

Answer 2

how would i find the 4th term? im confused with how the 1st and 2nd term went from 30 to the 3rd term being 15

Answer 3

The current term = previous term * r

Answer 4

2nd term = 1st term * 1/2
3rd term = 2nd term * 1/2
4th term = 3rd term * 1/2

Answer 5

so then 4th term would be 7.5*1/2=3.75 ?

Answer 6

yes.

Answer 7

You can also leave it as a fraction.
30, 15, 15/2, 15/4, 15/8, 15/16, ... will be the geometric sequence.
The fourth term is all they want and so it is 15/4

Answer 8

oh okay thanks! :)

Answer 9

welcome.