You are riding your bike to the mall. you travel the first mile in 10 minutes. the last mile takes you 15 minutes. this is an example of

If the person if slowing down, then this would mean that this would actually be "negative acceleration". Sense this person first did a mile in 10 minutes, and then the next mile that this person did was actually 15 minutes, then this shows you that they actually went a lot slower. And this is why this would be a great example of "negative acceleration".

Independent variable is something that is changed in a experiment.