investment question

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purplemonkey

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Sep 20, 2005
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ok... so i am not trying to take advantage of you all...but i might have a few questions tonight....so glad a found this webiste today, you are saving my husband and i from another night of math homework frustration....
me- "can you help me with this"
husband- follows with vague answer or confusing babble that makes me feel stupid...
me-"ahhhhhh"
:D
they should offer math class mariage counsling! Ah, but anyway....

an investment of $4600 is made at an annual simple interest rate of 6.8% how much additional money must be invested at an annual simple investment rate of 9% so that the total interest earned is 8% of the total investment....
I am not sure if i have the right idea with this one and I'd really like to be able to check my answer....this is what i've got

4600(.068)+.09x (x being the additonal amount invested)=(4600+x).08

312.8 +.09x=386+.08x
.01x=55.2
x=5520
so this makes sense to me....but can i check it?
 
To check the answer to any "solving" problem, plug your solution back into the original problem. If it "works", the solution is probably valid.

Eliz.
 
hmmm...i know i could check it by plugging it in as x...but i mean as a new equation....like where the problem says that the total is 8% of total invested? i think that has confused me
i worry with word problems that if the equation isnt correct in the first place the solution for x will not matter right?
 
You have a value for x. What does x stand for? How does this value relate to the original problem? (Labelling when you start can be important!)

Ignore your equation for a moment, and look back to the original problem. Does "5520" work there? Does it give you a solution that fits the problem? If you invest $4600 at 6.8% and this other amount at 9%, how much will you get back in interest? What is the total you invested? Is the interest you got equal to 8% of the total invested?

See if your answers are what they ought to be.

Eliz.
 
purplemonkey said:
312.8 +.09x=386+.08x
.01x=55.2
x=5520
so this makes sense to me....but can i check it?
Click to expand...

Just to make sure; is this the way you "checked" it:

4600 @ 6.8 = 312.80
5520 @ 9.0 = 496.80
total interest=809.60

4600 + 5520 = 10120
10120 @ 8.0 = 809.60
 
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