Anonymous asked:I was wondering if you had any tips to predict how a graph will be in the future (like page 295 in the collegeboard book)? Also, do you know when to add probabilities? Is that common on the sat?
In question 4 on page 295, they tell you to assume that the rate remains the same as it was from April to May (which is shown on the graph). So all you need to do is extend those lines and see what happens. Note that, if you weren’t told to assume that the rate remains consistent, you’d have no way to solve this question, since sales figures aren’t necessarily predictable.
As for adding probabilities, you can only do so when the events in question are mutually exclusive. For example, if there’s a lineup of people and one person is to be chosen from the lineup at random, the probability of any one person being picked is 1/10. If we’re trying to figure out the odds of me OR my brother being picked out of the same lineup, it’s 1/10 + 1/10 = 2/10. We add those probabilities because it’s not possible that we’d both be the one person picked. In other words, the events are mutually exclusive.
Probability questions on the SAT are pretty rare. There are only 7 in the 10 Blue Book tests, and none of them are classified as hard. That’s not to say you couldn’t get a hard one on your test, but it does indicate that it probably shouldn’t be your primary concern.