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Ok. So I go to these "summer school" SAT classes once a week. I don't really get why I go but then again, I’m getting these classes for free so I don’t really care…
This blog entry is about our SAT math “instructor” whose job is to basically teach us SAT math. So far he’s been doing a fucked up job imho. Just handing us practice math questions then answering them in front of us (thank God I’m not paying for this -_-).
Anyways, this morning during our SAT math session we were given a set of math questions, and as usual he answers them on his own in front of us. However, one of his answers was challenged by a couple of students. He denied the mistake and kept his answer. More students started seeing his mistake and soon after, the majority of the class agreed that he was wrong. He still claimed to be correct -___-. Please note, all students who challenged had the same answer. He didn’t have an answer key with him so we couldn’t check the correct answer to the question.
Now, I wanted to check with TL.net to see which one was right: the “instructor” or the students. It’s a simple problem. Here it is:
+ Show Spoiler +The Cyber Corporation buys a new machine for $80,000. If the machine loses 15% of its value each year, what is its value after 4 years? A)$41,760.50 B)$42,750 C)$43,350 D)$49,130 E)$57,800 + Show Spoiler +
Answers:
“Instructor”: D
Students: A
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Agreed with A.On August 09 2008 23:10 Plexa wrote:
wtf how can you even get D as an answer?
Was wondering that too. I tried making some obvious mistakes but the results weren't anywhere near these alternatives.
Edit: Wait...
80000*0.85^3 = 49130 -.-
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Calgary25996 Posts
A... unless there's some sorcery going on that I don't see...
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lulz, oh SAT classes
surprisingly, i learned a lot of math from them because my high school's oh-so-celebrated math program was bullshit
edit: yeah, A
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You guys are definitely right, ur teacher is a retard.
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The method the "instructor" had used was a geometric sequence
80000 * 0.85 ^(n-1)
The "instructor" says the answer is on the 4th year therefore n=4
80000 * 0.85^(4-1) = 49130
However the students' arguement was that the answer is AFTER 4 YEARS therefore on the 5th year so n=5
80000 * 0.85^(5-1) = 41760.5
+ Show Spoiler +(I got a 720 on my SAT math btw... I only come to this program for the english cuz i suck at critical reading and the essay T_T)
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Aotearoa39261 Posts
Yea thats exactly what i thought he did, although his reasoning sucks even more than my initial thought. The question quite clearly states "after" which implies that four full years have passed rather than it being any random date in the 4th year. Hence your teacher sucks
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On questions like these, I always go for the noob technique of actually punching in each step on the calculator (80000 x 0.85, ANS x 0.85, etc.).
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tracer, that's actually a really good technique to check your answers.
I remember on one test it asked:
the difference between the sum of odd numbers 11 and 31 and the sum of even numbers between 12 and 32. I used both formulas and brute force to solve. It gives me an assurance since I tend to make many simple mistakes.
On topic, Plexa has it. I think when the question asks "after four years, it means losing .15^4 percent. I guess one could argue that an end of four years means that the fifth has begun.
Just tell the instructor this. Even though your logic can be perfectly plausible on the SAT, follow what ETS says. Many questions, such as those in SAT II Bio, are like that.
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I'd decay 4 times, as it clearly says "after the 4th year"
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A is correct, no need to argue.
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Should be A.
80000 * .85 * .85 * .85 * .85
lol I feel kinda sorry for you having that kind of teacher
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technically it's not a math problem at this point but rather how you interpret the question
=/, obviously it's A , but anyone can argue its D with twisted logic, i blame lack of elaboration on SAT part
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On August 10 2008 03:16 HeavOnEarth wrote:
technically it's not a math problem at this point but rather how you interpret the question
=/, obviously it's A , but anyone can argue its D with twisted logic, i blame lack of elaboration on SAT part
Lack of elaboration? What are you talking about that question is about as clear as it gets, 15% decrease a year, what's the total decrease after 4 years. There's only one way to interpret that, any other way is reached through faulty logic.
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The instructor failed, but I understand how it could have happened. Most of us see the answer is A simply by relying on our intuitions. But the instructor cannot assume that everybody in his class has the intuition to do that problem. So he tried to show the mathematically correct to do it and got lost in the sauce.
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Actually, it is a lack of elaboration, and SATs usually make the wording clearer than that to avoid contests as to what the answer is. At that, all standardized tests make sure that the questions are to be tricky, but not vague in wording. If memory serves, SATs usually tack in sentences indicating that the 4 years would be 4 rounds of depreciation of value, rather than just saying "after four years", though I took mine before the change of the system, so perhaps they got laxer.
EDIT - I find it doubtful that the instructor attempted to show a mathematically correct way and got confused, or rather, if he tried to show such a method, he is an idiot in the first place. There is no place for mathematically correct solutions on standarized exams such as the SATs, rather, only intuitive and fast solutions are to be taught. If someone is actually following the method which problems are supposed to be solved for such exams and teaching them, then that person obviously have no understanding as to the workings of the exam. You don't get points for showing you know the principle, you only get marked for the solution.
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United States10774 Posts
haha you need a new instructor
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It seems like a really simple problem. I'd ask him to explain his answer I guess because the clear and obvious answer is A.
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United States24761 Posts
I agree that A is the more obvious interpretation.
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EPT
