Michael E. answered • 07/14/18

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College and High School Math for Classes and Test Prep

Hello Jeffy,

Based on the answer you say the book gave, here is how you want to type the original problem:

y = .9^(t-4).

Instead of using .7, use the actual value for .9^4 = .6561. Then, since it is in the denominator, you want:

1 / .6561, which gives you approximately 1.52.

Alternatively, approach it as follows:

Using properties of exponents, you can re-write as:

y = (.9^t) * (.9^(-4)) {Working in reverse, I am using that when multiplying like bases, you add the exponents}

If you throw .9^(-4) in the calculator, you get approximately 1.52.

So the equation becomes:

y = (.9^t) * (1.52)

→ y = 1.52(.9^t)

Hope the above helps, and thank you for posting the question.

Michael Ehlers

Michael E.

07/14/18