• Livestream AMA: Join SDN as we welcome Dr. John Ligon, a Pediatric Oncologist with the National Cancer Institute on May 11th at 8:00 PM Eastern. Register now!

polishp86

The Man, DDS
10+ Year Member
5+ Year Member
May 19, 2008
42
0
Status (Visible)
  1. Dentist
Ok guys here is my question, from the topscore pro software, test one, math question 19.

Mark has $7200 invested, part at 4% and the rest at 5%. if the annual income from both investments is the same, what is the income from his investment?

The answer is below:






























Let x = principle amt invested at 4%
let 7200 - x = principle amt invested at 5%
principle x rate = income

.04x = .05 (7200-x)

9x = 5(7200)

x=4000

4000 x .04 = income

income = 160

total = 160 x 2 = 320


I get all of the above, EXCEPT for where the 9x = 5(7200) is coming from. I know it's probably some simple calculation, but I am not seeing it for the life of me, and my test is in 2 days! crap!!!!!! I also do not understand how the -x has magically disappeared after the 7200.

anyways, I would appreciate any explanation for this, the topscore software doesn't do that great of a job explaning how it gets to certain conclusions/answers.

thanks in advance!
 

DrYoda

Space Cowboy
10+ Year Member
Jun 22, 2008
13,815
129
Dagobah System
Status (Visible)
  1. Attending Physician
It looks like they multiplied by 100 to get the decimals as whole numbers, distributed the 5 (previously 0.05) and then moved the 5x to give 9x.

0.04x=0.05(7200-x) multiply by 100 to get whole numbers

4x=5(7200-x) distribute

4x= 5*7200-5x add 5x to each side

9x=7200*5 divide each side by 9

x=4000
 
About the Ads
This thread is more than 12 years old.

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.