Luis went yesterday to the bank to find out the interest rate of three different financial instruments. He received the following information:
Financial instrument
Savings account
Certificate of Deposit (CD)
Bonds
Annual interest
2%
3%
4%
He wants to invest his USD 10,000 savings in these three accounts. By doing so, he knows that after a year he would receive a total of US 260 in interest if he put twice as much money in the savings account as in the CDs, and “z” money in bonds.
Calculate the value of “z” , in USD, using the elimination method explained in the lectures.
The first equation comes from knowing that the total sum that he invests into the three accounts is $10,000.
The second equation comes from knowing that the annual interest he receives from these three accounts is $260.
The third equation comes from knowing that he put twice as much money in the savings account as in CDs.
Once you have the three equations you can just throw the coefficients into a 3x3 matrix and hack away. Which of the three are you having difficulty figuring out?
I have the same problem and I don’t think I still got it clear. I answered this question and was incorrect and it’s very disappointing that there are no demonstrations of the correct way to solve this after you submit the answer and the system marks it as wrong.
My problem was not to solve a 3x3 matrix but to find the equations to compose the matrix… so… trying to translate the previous answer into the system of equations:
a + b + c = 10000
0.02a + 0.03b + 0.04c = 260
2a + b + c = 10260
Would that be the right? doesn’t seem quite right since the second one should reflect 0.04a (0.02 * 2) to get the 260 value (which makes the third line redundant).
Your third equation is a bit off. You just need an equation that indicates that he put twice as much money into savings as he did into CDs. No need to overthink it
Ok… I think I got it… it mentions that he has to put twice the money in the Savings than the CDs… and Z is the difference of that so it would be ok to say:
It’s even simpler than that. Z (or c, as you used in previous equations) has nothing to do with the final equation. Between a and b, one of those is twice the value of the other. Does 2a + b = 1 mean that one of the variables is twice the other? You’re getting warmer, but not quite there yet.
