How to prepare for PS calculations on test day

[axp107]

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Would it be a good idea to practice basic math/arithmetic. It seems like the general consensus is that the pS questions were not conceptually difficult. It's just that the calculations took forever...

So, its really just timing that matters in the end.. not how much you know.

 

[jochi1543]

Well, remembering how to manipulate logs for pH purposes would definitely help.

 

[artaxerxes]

get your SciNotation down, thats about it really. And know how to do long division.

 

[Kaydubz]

get your SciNotation down, thats about it really. And know how to do long division.

Use e 🙂, it saves time.

5e6 is much faster than 5 x 10^6
Just make sure you don't do something stupid like convert 10^5 to 10e5. It's 1e5

 

[corbis11]

make sure you know how to multiply and divide large numbers like 3x10^8/6x10^-14 😉

 

[Hindiana_Jones]

So thats it, practice your scientific notation and division? My main problem in physical sciences is doing the calculations quickly enough...I've been practicing from an old math book, but I still make mistakes sometimes...

 

[Nikki2002]

i think it may also depend on your form as well whether you get a PS section that is heavy on calculations or heavy on concepts. When I took it last August there were surprisingly few calculations--and they were simple. I mean trust me--I could do them so they were simple. The rest tested concepts

 

[wisguy]

Like above posters said, they mostly test division/multiplication of sci notation or very simple arithmetic. If it seems harder, you're probably missing something (often they are testing a relationship- if you double x with everything else constant, what is y -you don't need to calculate everything in this case, just determine what is the effect of doubling x) I think the toughest calc that I had was to find the change in PEgrav. Ok, not really, but it was close.

 

[Alshera]

According to the EK books, you should utilize rounding as well, and make sure if you round one number up in a calc. you should round the other down, etc. I would recommend looking at the EK calc. help passage in the EK Verbal book. I'm terrible at math, but those suggestions are really helpful.

 

[Hindiana_Jones]

From a fellow person concerned with calculations:
I did a search for math in the MCAT forum, got this great website:

http://www.premed411.com/pdfs/math.pdf

More PDFs on this page: http://www.premed411.com/e-znotes.html

Print out this PDF and go through it, its got what you need to know.
Also, buy Nova physics off amazon (its $20.00 cheaper than Borders) and do the first chapter. Actually, do the whole book, but the first chapter is good for math. I've done half of the problems from the first chapter and I feel better about it already.

Convert decimals to fractions when doing arithmetic, they are easier to manipulate.


Understand how things are directly related and inversely related, Nova physics chapter 1 is great for this. Realize to test a relationship you will have to make a proportion between the two equations if you cannot see how they will change immediately. If two values are directly related, say X= (1/3)T^2 and T increases by 6, and you want to know how much x will increase by, it will increase by a factor of 36, b/c 6^2 is 36. The (1/3) is irrelevant. If this is difficult to see do the following:

X= (1/3)T^2 / X= (1/3)T^2 and see that the 1/3 cancels.


Memorize the values of sin and cos from 0 to 180 degrees in both fractions and decimals (very quick in decimals)

Sin 30= .5 Cos 30 = .9
Sin 45= .7 Cos 45 = .7
Sin 60= .9 Cos 60 = .5

COS OF ZERO IS ONE! SIN OF ZERO IS ZERO!
This is important, especially when you do W =Fdcosθ, et al.

Note that the values for sin are the same values for cosin flipped.

Vectors are added starting at the TIP of the first vector (the arrow) and placing the TAIL of the SECOND vector at its tip (I have had some trouble with that). So always start at the HEAD of the first vector.


Memorize that the square root of 2 =1.4 and the square root of 3 = 1.7

I read a lot to practice your long division.

I read this explanation in one of the threads when I did a search, it was helpful:
A logarithm is a way of expressing a number as a power of ten.

 

[Hindiana_Jones]

Useful threads:

GREAT thread on logs:
http://forums.studentdoctor.net/showthread.php?t=398458&highlight=math

Also:

good point. you should be confident with something like
-log(4x10^-3)

since this is right from the pH eqs. remember:
-log(4.0x10-3) = -log(4) + -log(10^-3)
= -log(4) - (-3)

-log(4) is another way of saying 10^x = 4. x=?
well, 10^0.5 is around 3.2, so x must be higher than 0.5, like 0.6.
so -log(4x10-3) = -0.6 + 3 = 2.4

From:http://forums.studentdoctor.net/showthread.php?t=109738&highlight=math

remember it like this,

log x = n then x = 10^n

log x = 1 then x = 10
log x = 2 then x = 100
log x = 3 then x = 1000

From:http://forums.studentdoctor.net/showthread.php?t=116005&highlight=math

The easiest and cheapest way to address this is by borrowing an Algebra II/Trig book from your local library. And just practice.

Don't forget "SOH CAH TOA" (eg Sin = Opposite over Hypotenuse).

For square roots, you should just memorize the squares of the most common ones (most mcat prep books will tell you to do the same).
Square of 4 = 16
Square of 5 = 25
Square of 6 = 36
Square of 7 = 49
Square of 8 = 64
Square of 9 = 81
Square of 10 = 100
Square of 11 = 121
Square of 12 = 144
Square of 15 = 225
Square of 25 = 625

From: http://forums.studentdoctor.net/showthread.php?t=352507&highlight=math

Also:http://forums.studentdoctor.net/showthread.php?t=188301&highlight=math
http://forums.studentdoctor.net/showthread.php?t=284656&highlight=math

 

[Funky]

I don't remember doing a lot of number crunching in the mcat for the PS section. If you needed a sin/cos of something they gave it to you. I guess the most important thing is to just learn sci notation and how to estimate log.