Hello! Well this is actually quite simple. You always have to have more than one variable in order to manipulate or change a certain situation. Two Variables would be the least amount however you could have up to 4 and even more possibly. An example would be how time and speed are related. With these so variables this would be able to make a prediction because it would show the distance a car may be driving. If you only have the distance and the time, this can help you predict the average speed a car might be going. Hope this helped!! :)