Which series are neither arithmetic nor geometric?

Question

Which series are neither arithmetic nor geometric?

Choose all answers that are correct.

 

Choice 1-   4 + 40 + 400 + 4000 + 40,000 + . . .

Choice 2-  4 + 40 + 44 + 84 + 6128 + . . .

Choice 3-  –4 + 20 – 100 + 500 – 2500 + . . .

Choice 4-  –4 + 20 – 40 + 200 – 400 + . . . 

Answer 1

In an arithmetic series the same number is added each time.

None of the choices show that. So all of them are not arithmetic.

 

In a geometric series the same number is multiplied each time.

In choice 1 each number is multiplied by 10. It is geometric.

In choice 3 each number is multiplied by -5. It is geometric.

 

Neither choices 2 and 4 have the same number or multiplied each time.

Choices 2 and 4 are neither arithmetic nor geometric series.