http://sat.collegeboard.org/practice/sat-question-of-the-day?src=R&questionId=20130305 (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 B. This is a pretty simple question and you can look at how many students are getting it right (69% at 5:30AM Eastern Time) to see that. The SAT explanation is good at how to do the algebra. However, I’m a little concerned about their substitution using 1 as part of the explanation. Here’s the problem.
Substituting 1 happens to work but substituting other numbers may not work, for example 2 or 5. If you substitute 2 or 5 into the equation 10x – 5, you get 15 for an answer (E) as well as 5 (B). That means you get two right answers!! It is easy enough to take another step and try a different substitution. 3 works to eliminate E; so, you get B. I think they should have warned you about that. Furthermore, substituting 1 on some SAT and ACT questions leads to this very same problem of getting two answers. Now, if you’re new to my blog, you are probably beginning to think that I don’t like substituting numbers for variables on the test. That’s a long ways from being true!
I love this technique. I even have several names for it: change the abstract to the concrete, substitute numbers for variables, convert the algebra to arithmetic. It is a great technique that works for about 20% of the SAT math questions. Anytime an SAT or ACT question doesn’t give you numbers but gives you a rule about the variable or unknown (“x is a positive integer” in today’s question”) you can make a number up following the rule. That’s because the world of math is a world of patterns. All my students become experts at using this strategy because it will dramatically raise scores. While I love the strategy, I’m just not enchanted with half-hearted explanations like the one the SAT folks gave you this morning. It may be misleading for many students.
Let’s move on and see what the ACT folks are up to 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.)-
Will everyone please send the ACT folks an email and tell them to get some new material? Just kidding! However, I do wish the ACT staff would do that.
The answer is G. Their explanation isn’t bad for the right answer. However, this question isn’t going to be on the test; so, let’s see what we can learn about the ACT by using this question as an example. First, don’t do any science knowledge review because you couldn’t possibly predict what science is going to be on the test and they explain all the science facts you need to answer the question anyway. Second, sometimes wrong answers (distractors) are just nitpicking reading issues: answer A is eliminated because of the difference between “bare rock” and “bare field.” Third, don’t make any assumptions. The field may have some bare rock places but we aren’t told that. Don’t use what you know may be true; base your answers on what they tell you to be true. Third, some wrong answers (J in this case) will be exactly the opposite of the data you are given. Be careful. Finally, practice reading data and expect to see charts like you’ve never seen before. This is a good example. I suggest getting your hands on some actual ACT tests and reading the data presentations so you get faster at understanding how data is presented. The Real ACT Prep Guide is the best source.
As always, I want you to understand doing the Questions of the Day is a good thing. The real value in doing them is learning what you can about the test–not simply doing this particular question because it will never be on the test you take.
If you aren’t registered for your test date, do it NOW. Seats are filling up and you could get sent to an alternative test location. That’s not much fun on test morning.
Have a good day!