# urgen linear equation help INVESTMENTS gr. 10!

• Jan 19th 2009, 06:18 PM
xo-sherry
urgen linear equation help INVESTMENTS gr. 10!
hey
im having an issue with a word problem for investments (linear equations)
any tips on how to solve these?

for example this one:
a principal of \$2500 is invested; part at 8% annum and the rest at 12% annum. In one year, the two investments earned equal amounts of interest How much was invested at each rate?

im having my exam tomorrow so yah
any tips for linear equations will be appreciated!!!!

and also i heard there was a forumla for investments. would anybody mine explaining to me what it is? and hwo does it work?

thanks!
• Jan 19th 2009, 06:33 PM
mollymcf2009
Investment formula: ONLY works for simple annual interest NOT compounding interest!! VERY important!

I=Prt, where I is the interest earned on the original investment

This is what you are trying to find.

P = amount of original investment

r = annual interest rate

t = time period in years **IMPORTANT: for 1 year, t = 1. If you are asked for just PART of a year, you must divide those number of months by 12 months. For example, if the question asked you for 9 months of interest, t would = 9/12 or .75 years. Got it?

So, you should be able to use the data you are given in the problem and the two equations to figure this out. Come back if you are still stuck.
Good luck on your test!
• Jan 19th 2009, 06:53 PM
xo-sherry
Quote:

Originally Posted by mollymcf2009
Investment formula: ONLY works for simple annual interest NOT compounding interest!! VERY important!

I=Prt, where I is the interest earned on the original investment

This is what you are trying to find.

P = amount of original investment

r = annual interest rate

t = time period in years **IMPORTANT: for 1 year, t = 1. If you are asked for just PART of a year, you must divide those number of months by 12 months. For example, if the question asked you for 9 months of interest, t would = 9/12 or .75 years. Got it?

So, you should be able to use the data you are given in the problem and the two equations to figure this out. Come back if you are still stuck.
Good luck on your test!

hi
im sorry but i still can't get the answer. i got 200 of 8% and 300 of 12%
and i dont get how we can use this formula to formulate 2 equations...
im really sorry to bother you.
• Jan 19th 2009, 07:36 PM
mollymcf2009
Ok, see if this helps you. Sorry I took so long, I'm doing homework and this.
Sometimes I make a table to get all my data down. I can't really do that here but I'll try to line things up the best I can. *The data for each interest rate is listed from left to right. Hope this is understandable:
This is a layout of the I = Prt equation I gave you earlier:

Interest Rate ----------Interest earned ------- ---------- Principal --------------- rate ------- time

8% --------------------------.08x ------------------------- x----------------- .08 ---------- 1 year

12% --------------------(\$2500-x)(.12) --------------- \$2500-x ------------.12 -------------1 year

Do you understand how I set this table up? I decided to find the amount for the 8% chunk first. So, I know that .08x is going to be the interest that THIS amount of money will make at this interest rate. The principal is that unknown amount of money (x). .08 is the rate etc.
Since I have to have an exact answer for one of the rates before I can find the other, 12% chunk of money will depend on whatever 8%'s chunk is.

So I set up my equation to find this, directly from the table:

.08x = (\$2500-x)(.12)
.08x = 300 - .12x
.08x + .12x = 300
.2x = 300
x = \$1500 This is how much was invested at 8%
Now, you should be able to find out how much was invested at 12%.
**The amount of interest isn't really important and the question isn't asking for that, but you could find it if you needed to.

Good now? Come back if you're still stuck and we can try something else.
**If you ever get stuck on a problem like this or any other kind of problem first write down all of the information the problem gives you. Word problems add unnecessary words that get people confused. If you can just take the information out that you need, it can usually make a seemingly difficult problem much easier.
Good luck!!
• Jan 19th 2009, 09:03 PM
xo-sherry
Quote:

Originally Posted by mollymcf2009
Ok, see if this helps you. Sorry I took so long, I'm doing homework and this.
Sometimes I make a table to get all my data down. I can't really do that here but I'll try to line things up the best I can. *The data for each interest rate is listed from left to right. Hope this is understandable:
This is a layout of the I = Prt equation I gave you earlier:

Interest Rate ----------Interest earned ------- ---------- Principal --------------- rate ------- time

8% --------------------------.08x ------------------------- x----------------- .08 ---------- 1 year

12% --------------------(\$2500-x)(.12) --------------- \$2500-x ------------.12 -------------1 year

Do you understand how I set this table up? I decided to find the amount for the 8% chunk first. So, I know that .08x is going to be the interest that THIS amount of money will make at this interest rate. The principal is that unknown amount of money (x). .08 is the rate etc.
Since I have to have an exact answer for one of the rates before I can find the other, 12% chunk of money will depend on whatever 8%'s chunk is.

So I set up my equation to find this, directly from the table:

.08x = (\$2500-x)(.12)
.08x = 300 - .12x
.08x + .12x = 300
.2x = 300
x = \$1500 This is how much was invested at 8%
Now, you should be able to find out how much was invested at 12%.
**The amount of interest isn't really important and the question isn't asking for that, but you could find it if you needed to.

Good now? Come back if you're still stuck and we can try something else.
**If you ever get stuck on a problem like this or any other kind of problem first write down all of the information the problem gives you. Word problems add unnecessary words that get people confused. If you can just take the information out that you need, it can usually make a seemingly difficult problem much easier.
Good luck!!

thank you so so so so much! (Rock)
i really appreciate the time you took to help me!
thank youu!! and again i apoligize for bothering you!