I need help with sequences

Question

2,1,1/2,1/4,...

Is this arithmetic, geometric,neither, or both (geometric?)

7,9,11,13
arithmetic, geometric,neither, or both.
(arithmetic?)

1,2,4,8...

Whats the rule think the rule is: Start with one and multiply by two repeatedly

50,40,30,20

Rule Start with 50 and subtract ten repeatedly

Find the next three terms in the sequence

1,1,2,3,5,8..(11,14,17)

I put my answers, can someone please check them?

Thanks in advanced

Answer 1

The first 4 are all ok.

The last one is the Fibonacci Sequence, where each term is the sum of the two previous terms. It goes

1,1,2,3,5,8,13,21,34,55,...

Your constant d=3 is just based on the terms 5,8 but clearly does not hold for the earlier terms.

Answer 2

I'm confused :|