A rule for estimating the number of board feet of lumber that can be cut from a log depends on the diameter of the log. To find the diameter, $d$, required to get 5 board feet of lumber, we use the equation $\left(\frac{\mathrm{d}-4}{4}\right)^{2}=25$. Solve this equation for $\mathrm{d}$. Are both answers reasonable?
A) $\{20,-20\}$; No, only 20 feet is a reasonable answer.
B) $\{24,-16\}$; No, only 24 feet is a reasonable answer.
C) $\{9,-20\}$; No, only 9 feet is a reasonable answer.
D) $\{16,-24\}$; No, only 16 feet is a reasonable answer.

Question

Quizplus · Accepted Answer

Solving the equation $\left(\frac{\mathrm{d}-4}{4}\right)^{2}=25$ gives $\frac{\mathrm{d}-4}{4} = \pm5$. Solving for $d$ gives $d = 24$ or $d = -16$. Since the diameter of a log cannot be negative, only 24 feet is a reasonable answer.

A Rule for Estimating the Number of Board Feet of Lumber