Answers:
a) geometric
b) arithmetic
c) arithmetic
d) geometric
Explanations:
An arithmetic sequence is a when the next term is achieved by adding/subtracting by a constant (the same number) to the current term.
A geometric sequence is a when the next term is achieved by multiplying/diving the current term by a constant. (i.e. the ratio between any two consecutive terms is the same for any other two consecutive terms).
a) The numbers are all products of the previous term by a multiple of 2 (i.e. each term is multiplied by 2 to get the next term).
b) The numbers increase by the same amount between every term (by 3 in this case).
c) The numbers increase by the same amount between every term (by 5 in this case).
d) The numbers are all products of the previous term by a multiple of 10 (i.e. each term is multiplied by 10 to get the next term).