crindo2 wrote:

This is my first topic so please be kind. The question below is an IR question that I am having trouble setting up. Any input from members would be greatly appreciated.

Hi Crindo,

You're looking at a classic mixture problem--you can check out

here for a little more detail on them.

Basically, we are "mixing" 4% and 8% interest, to get

r% interest. Although this problem is discussing interest rates, we shouldn't be distracted, because we don't need any fancy formulas for calculating them. We can use the mixture formula alone--which is, conveniently, given to us by the question stem!

r is given to us as 5%, so we can plug that in to the mixture formula given in the question stem. Do so, then remove fractions:

5(

x + y) = 4

x + 8

yDistribute:

5

x + 5

y = 4

x + 8

yCombine like terms:

x = 3

yNow, many TPA problems will not have a single algebraic solution. This is two variables in one equation; it's unsolvable. But we have a limited number of choices to solve for. Plug them in, and we'll find that the only set of answers that works is

x = 96,

y = 32

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Eli Meyer

Kaplan Teacher

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