1. 7,9,11,13
a arithmetic
b geometric
c both
d neither

2. 2,1, 1/2 1/4
a arithmetic
b geometric
c both
d neither

3. 1,2,4,8
a start with 1 and then add 1 repeatedly
b start with 1 and then add multiples of 2 repeatedly
c start with 1 and then multiply by 2 repeatedly
d start with 1 and then divide by 2 repeatedly

4. 50,40,30,20
a start with 50 and then add 10 repeatedly
b start with 50 then add -10 repeatedly
c start with 20 and then add 10 repeatedly
d start with 50 and then add multiples of 10 repeatedly