Algebra help please!!?

Question

I'm really struggling with the geometric sequences:/ If you could help me and explain I would really appreciate it:)
1.Determine if the sequence is arithmetic or geometric. Then find the next term in the sequence. Select all that apply.

8, 5, 2, -1, -4, …

A.arithmetic
B.geometric
C.-10
D.-7

2.Find the common ratio, r, in the following geometric sequence.

27, 9, 3, 1, …

A.3
B.-3
C.1/3
D.-9

Answer 1

1)Given series is 8, 5, 2, -1, -4, …

The common difference between any two terms is -3.

=> d =-3

First term t1 = a =8

We have to find the 6th term =>          [Formula for nth term]

                                                        

                                                               = 8 + 5(-3)

                                                               = 8 - 15

                                                               = -7

Therefore the next term in the series is -7

Therefore the answer is D

Answer 2

2) Given geometric series is 27, 9, 3, 1, …

     Common ratio r = t2 / t1  where t1 = first term and t2 = second term

                                   = 9 / 27

                                   = 1/3

     Therefore the common ratio is 1/3.

      Therefore the answer is C.