mathiaskeul wrote:
One thing I have to say. Is there like a way to know which formulas to use with which questions apart from the videos? I rarely know where to start.
Also I keep making stupid mistakes by not reading the question correctly or doing one small error in the calculation....
For instance
In the xy-coordinate system, points (2, 9) and (-1, 0) lie on line k. If the point (n, 21) lies on line k, what is the value of n?
I think I have to find the equation y=mx+b, but with a slope of 9/3 i get the answer 7 while it should be 6. so my reasoning always seems to be a bit off and no matter how many exercises i make it just seems so freagin hopeless...
Dear
mathiaskeul,
I'm happy to respond.
First of all, using formulas correctly is about 5% of what you need to know and understand for GMAT math. Folks get really attached to formulas and don't realize that, after a very basic level, the attachment to formulas can hinder them.
Formulas are like tools in a tool box. It's good to have a functioning tool box, but that's not the whole story. The poor workman always wants to use his tools. The master craftsman knows when to use his tools and when to work with his hands. Mastering GMAT math is like being that master craftsman with respect to the formulas: knowing when to set the formulas aside and knowing when to employ them skillfully.
For example, in that math problem you quoted, I think it's a mistake to get the slope purely relying on the "slope formula." That's asking for trouble. What I recommend in the
Magoosh videos is to visualize the slope, sketching out a slope triangle.
Attachment:
slope triangle.JPG [ 23.92 KiB | Viewed 2883 times ]
You don't understand slope unless you understand it visually. Since rise = 9 and run = 3, we get slope = (rise)/(run) = 9/3 = 3.
Now, we could use a formula, but let's boycott formulas for this solution. What does a slope of m = 3 mean? Among other things, it means "
move to the right one unit and move up three units." Let's start at (2, 9) and move that way.
(2, 9) --> (3, 12) --> (4, 15) --> (5, 18) --> (6, 21)
There's our answer, without any formula. I think you are limiting yourself by over-reliance on formulas. Use of formulas is a very small part of what you need to understand for GMAT math. What I have shown here, thinking about the coordinate plane visually, is much more important.
Here's a blog article that might interest you:
Careless Mistakes on GMAT MathYou will notice that in the links I posted a couple days ago, those articles are about stress reduction, but the mindfulness techniques also build focus. Practice seeing every detail in your environment, and this will support you in seeing carefully every detail of a GMAT problem. Pay attention to all the small details as if your life depended on it, because the truth is, if your life is going by and you don't see any of the details, you don't really own your own life.
Does all this make sense?
Mike