# Method of elimination practice quiz, Q7 (can't solve)

Sorry but I can’t work out how to calculate the answer to this final question in the method of elimination practice quiz. Could someone advise me please? Thank you!

It took me a while to figure this out.

The key is that there appear to be three variables and only two equations, but in fact there are only two equations and two unknows.
x = savings amount
y = cd amount
z = bond amount

The facts in the statement give you two relationships:
x + y + z = 10000
x = 2y
So you substitute for x and you get:
`1) 3y + z = 10000`
That’s the first equation.

Then you compute the amount of interest.
that’s:
0.02 * x for savings, 0.03 * y for cd, and 0.04 * z for bonds, and they sum to 260.

Substituting again x = 2y and simplifying, you get the 2nd equation:
`2) 0.07y * 0.04z = 260`

Now you can use elimination on equations 1) and 2) to find the results for y and z,
then use x = 2y to find x.

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Thank you so much for explaining that to me. I just went back through it with your notes + the relevant video for help and I actually managed to get the right answer doing it by myself this time