HELP PLZZZ????? 30 points???

1. What is the missing term ,a, in the pattern below?

20, 10, a, 2.5, 1.25,...

a. 5

b. 0

c. 10

d. 7.5


2. Which expression describes the rule for the pattern below?

3, 9/2, 6, 15/2, 9,...

a. multiply by 1/2

b. add 3/2

c. multiply by 3/2

d. add 3


3. What is the missing term ,x, in the pattern below?

1, 8, x, 64, 125,...

a. 27

b. 56

c. 32

d. 15