Question
A county realty group estimates that the number of housing starts per year over the next three years will be $$H(r)=\frac{300}{1+0.03 r^{2}}$$where $r$ is the mortgage rate (in percent).a. Where is $H(r)$ increasing?b. Where is $H(r)$ decreasing?
Step 1
The quotient rule states that the derivative of $\frac{f(x)}{g(x)}$ is $\frac{f'(x)g(x) - f(x)g'(x)}{[g(x)]^2}$. So, the derivative of $H(r)$ is: $$H'(r) = \frac{0 \cdot (1+0.03r^2) - 300 \cdot (0.06r)}{(1+0.03r^2)^2}$$ Show more…
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A county realty group estimates that the number of housing starts per year over the next three years will be $$H(r)=\frac{300}{1+0.03 r^{2}}$$ where $r$ is the mortgage rate (in percent). a. Where is $H(r)$ increasing? b. Where is $H(r)$ decreasing?
A study prepared for the National Association of Realtors estimates that the number of housing starts per year over the next 5 years will be $$N(r)=\frac{7}{1+0.02 r^{2}}$$ million units, where $r$ (percent) is the mortgage rate. Use differentials to estimate the decrease in the number of annual housing starts when the mortgage rate is increased from $6 \%$ to $6.5 \%$.
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A study prepared for the National Association of Realtors estimated that the number of housing starts per year over the next 5 years will be $$N(r)=\frac{7}{1+0.02 r^{2}}$$ million units, where $r$ (percent) is the mortgage rate. Suppose the mortgage rate $t$ months from now will be $$r(t)=\frac{5 t+75}{t+10} \quad(0 \leq t \leq 24)$$ percent/year. a. Find an expression for the number of housing starts per year as a function of $t, t$ months from now. b. Using the result from part (a). determine the number of housing starts at present, 12 months from now, and 18 months from now.
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