Math Problem Shortcuts for the SAT!!!

Discus: SAT/ACT Tests and Test Preparation: March 2004 Archive: Math Problem Shortcuts for the SAT!!!
 By Chumboy87 (Chumboy87) on Tuesday, March 23, 2004 - 06:35 pm: Edit

Ok, here is the post where we all give out little shortcuts for harder math problems on the SAT. Please post yours!!! I have two.

1)If you need to find the average speed for two different speeds with the same distance covered (i.e. somebody driving to work 50 m/s and then driving back 45 m/s, find the avg. speed), consider A the first speed and B the second, use this formula: (2AB)/(A+B) (note: you don't need to know distance traveled!)

2)If you need to find the area of a triangle but you only know the three sides, don't find the height, use Hero's formula!
A=1st side; B=2nd, and C=3rd

Area=[square root](S(S-A)(S-B)(S-C)), where S=(1/2)(A+B+C).

 By Arow (Arow) on Tuesday, March 23, 2004 - 09:00 pm: Edit

about Hero's formula(I thought it was Heron?), it takes a long time to plug in the numbers. I think its easier and faster to use the normal way to calculate the area.

The one for the speed problem is great !

 By Osnapjew (Osnapjew) on Tuesday, March 23, 2004 - 09:30 pm: Edit

make a simple TI-83+ program for Heron's

INPUT A
INPUT B
INPUT C
.5(A+B+C) [STO] S
(S*(S-A)*(S-B)*(S-C)) [STO] X
DISP X

 By Scion (Scion) on Friday, March 26, 2004 - 06:44 pm: Edit

this is a good thread. anyone else have any tips before tomorrow?

 By Crypto86 (Crypto86) on Friday, March 26, 2004 - 08:43 pm: Edit

You forgot the total radical on the 5th line of code. Should be:

Sqrt((S*(S-A)*(S-B)*(S-C))) [STO] X

 By Crypto86 (Crypto86) on Friday, March 26, 2004 - 08:47 pm: Edit

Bah - I get Error:Archived...

I always get those on programs I download. Anyone know how to get rid of them/what they mean?

 By Tired_Student (Tired_Student) on Friday, March 26, 2004 - 09:01 pm: Edit

bah this doesnt work, just wasted my time

 By Aim78 (Aim78) on Friday, March 26, 2004 - 09:39 pm: Edit

When you have a repeating decimal and you have to find a certain digit, you use remainders:

In the repeating decimal 0.235235235235, what is the 457th digit?

1.) 457/3 = 152 Remainder 1 (divide by 3 because there are 3 digits repeating)
2.) Remainder 1 means it will be the first digit. Remainder 2 means it will be the second digit. And remainder 0 means it will be the third digit.

The 457th digit is 2.

 By Aim78 (Aim78) on Friday, March 26, 2004 - 09:49 pm: Edit

Lets say there are 6 roads from A to B, 4 roads from B to C, and 8 roads from C to D. You drive from A to D, passing through B and C, and back, passing through B and C again, and not driving on the same road twice. How many possibile routes are there?

6*4*8*7*3*5 = 20160 possible routes

 By Hobbes344 (Hobbes344) on Friday, March 26, 2004 - 09:57 pm: Edit

That is only when you're working with decimals though, isn't it?

 By Scion (Scion) on Saturday, March 27, 2004 - 12:01 am: Edit

last minute tips?! sorry i dont have many...

 By Aim78 (Aim78) on Saturday, March 27, 2004 - 12:07 am: Edit

I think the best way to study for the math portion is to look at all the types of problems that appear, and understand how to solve all of them. The majority of the questions are patterned after past ones, with maybe a few exceptions. They should make a book with all the types of math problems that have appeared, and general solutions to them.