Which pattern could be used to create the sequence?
400, -200, 100, -50, 25
a) multiply the previous term by -2
b) divide the previous term by -2
c) subtract 600 from the previous term
d) add -200 to the previous term

As you are given multiple choice, you can use trial and error with each of the answers. You can see that with each number the sign before it is reversed (so it goes even, odd , even , odd etc.) and the numbers are halved each time. 
The answer is B) because you are dividing by 2 each time, and changing the sign before the number.