A Rule for Estimating the Number of Board Feet of Lumber

Multiple Choice

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.