The value \( V \) of a certain automobile that is \( t \) years old can be modeled by \( V(t)=14,576(0.84) \). According to the model, when will the car be worth each of the following amounts? (a) \( \$ 7000 \) (b) \( \$ 6000 \) (c) \( \$ 4000 \)
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To find when the car will be worth the specified amounts, we set up the equation \( V(t) = 14,576(0.84)^t \) and solve for \( t \). (a) For \( V(t) = 7000 \): \[ 7000 = 14,576(0.84)^t \] Dividing both sides by 14,576: \[ 0.84^t = \frac{7000}{14,576} \approx 0.479 \] Taking the logarithm of both sides: \[ t \cdot \log(0.84) = \log(0.479) \] Now solving for \( t \): \[ t = \frac{\log(0.479)}{\log(0.84)} \approx 3.56 \] So, the car will be worth $7000 in about 3.56 years. (b) For \( V(t) = 6000 \): \[ 6000 = 14,576(0.84)^t \] Dividing both sides by 14,576: \[ 0.84^t = \frac{6000}{14,576} \approx 0.411 \] Taking logarithms: \[ t \cdot \log(0.84) = \log(0.411) \] Now solving for \( t \): \[ t = \frac{\log(0.411)}{\log(0.84)} \approx 4.51 \] So, the car will be worth $6000 in about 4.51 years. (c) For \( V(t) = 4000 \): \[ 4000 = 14,576(0.84)^t \] Dividing both sides by 14,576: \[ 0.84^t = \frac{4000}{14,576} \approx 0.274 \] Taking logarithms: \[ t \cdot \log(0.84) = \log(0.274) \] Now solving for \( t \): \[ t = \frac{\log(0.274)}{\log(0.84)} \approx 5.78 \] So, the car will be worth $4000 in about 5.78 years.