http://sat.collegeboard.org/practice/sat-question-of-the-day?src=R&questionId=20130128 (This link takes you to today’s question. If you use my archive, you will see the question related to my SAT explanation for that date.)
The answer is C. When taking the SAT and ACT, keep in mind a couple of things you learned early in your math career: multiplication and division by zero. The test writers like to see if you recognize them in different kinds of ways. This is a perfect example of something you know; you can’t divide by 0. That means if x=c, then the denominator is 0 and you can’t divide which causes the function to be undefined. That’s a simple math rule you learned long ago and the problem is the test writers are very cunning when it comes to presenting you with word problems that are different than you’ve seen before. Be cautious.
Another case of “undefined” that shows up on the tests is slopes. Remember that slope is defined as rise/run or change in y/change in x. If x doesn’t change, then the run is 0 and you have an undefined slope.
Let’s see what the ACT folks have in store for us this morning.
http://www.act.org/qotd/ (The ACT staff does not put a date on their questions so if you click on an archived blog, you’ll get today’s question and the old explanation. Sorry. The SAT staff has dated their questions; so, the archive is helpful. The ACT folks simply don’t do that.)
The answer is F. This is a great example of two things you need to always keep in mind about the ACT Science test. First, you don’t need to worry about knowing any specific science knowledge–they give it to you. In this question, you don’t need to know what chemicals the symbols (just match the letters!) represent, they explain pH, etc. It is simply a matter of reading charts and graphs when you are asked questions. They tell you to find a place on the table that has low Fe2+ and if you don’t misread and pick the Fe3+ column, you are all set. Then match the concentration of O2 and pH from the question to the table. That is just so typical of many questions on the test. Just read carefully and move on.
Second, time is an issue. You have to go quickly in order to finish on time. When you see the graphs and table, don’t waste time trying to learn them. Just get an idea of what they are about and let the questions guide you. In this case, you can see as you go deeper that the temperature warms up and that the concentration of different chemicals is given. That’s all you need to know before you get to the questions. Don’t focus on the details until you get to the questions. For example, pH is getting more acidic as you go deeper. Don’t even bother with the other columns on the chart now that you know things are changing as you get deeper. The questions will tell you what part of the table is important. At a depth of 0, you get the conditions that are described in the table.
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If you are taking the February ACT, time is running short. I recommend you watch my online Tips and Tricks videos to help you prepare. In addition to the free ones on the home page, it only costs $3 to watch an hour of my best test-taking techniques for taking the SAT and ACT tests.