Value: 8

What base could be written in the blank to make the exponential function model \( 15\% \) decay?

[tex]\[ y=(\ldots)^{\frac{t}{12}} \][/tex]



Answer :

Sure! Let's find the base for an exponential function that models a 15% decay.

When dealing with exponential decay, the general form of the exponential function is:
[tex]\[ y = \left( b \right)^{\frac{t}{12}} \][/tex]
where \( b \) is the base we need to find, and \( t \) represents time.

1. Understanding the decay rate: A 15% decay implies that each unit time period, the quantity reduces by 15%. This means after one time period, 85% (which is \(100\% - 15\% = 85\%\) or \(0.85\) as a decimal) of the original amount remains.

2. Relating decay rate to base: The base \( b \) corresponds to the fraction of the quantity that remains after each unit time period. For a 15% decay per unit time period, the remaining portion is \( 0.85 \).

3. Exponent time frame adjustment: Since we are considering decay over a period of \( \frac{t}{12} \), and we want to find the equivalent base that describes decay each month, we need the base \( b \) such that:
[tex]\[ b = 0.85 \][/tex]

So, the base that models a 15% decay in the exponential function \( y = \left( b \right)^{\frac{t}{12}} \) is:

[tex]\[ b = 0.85 \][/tex]

Therefore, the function can be written as:

[tex]\[ y = (0.85)^{\frac{t}{12}} \][/tex]

So, the value that should be placed in the blank to model a 15% decay is [tex]\( \boxed{0.85} \)[/tex].

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