Official Solution: Alpha Optics and Beta Vision buy high-precision optical lenses from the same manufacturer. The price of a lens is inversely proportional to the cube of its diameter. Alpha Optics buys 30 lenses, each with a diameter of 6 mm. Beta Vision buys 90 lenses in total: 30 lenses with a diameter of 3 mm, 30 lenses with a diameter of 2 mm, and 30 lenses with a diameter of 1 mm. How many times as much does Beta Vision pay as Alpha Optics?A. 80
B. 120
C. 180
D. 251
E. 300
Since the price of a lens is inversely proportional to the cube of its diameter, the price of a lens with diameter \(d\) mm can be written as \(\frac{k}{d^3}\), where \(k\) is a constant and \(d\) is the diameter in mm.
Alpha’s total cost is:
\(30 * \frac{k}{6^3} = 30 * \frac{k}{216}\)
Beta’s total cost is:
\(30 * \frac{k}{3^3} + 30 * \frac{k}{2^3} + 30 * \frac{k}{1^3}=\)
\(= 30(\frac{k}{27} + \frac{k}{8} + k)=\)
\(= 30 * \frac{251k}{216}\)
Therefore, \(\frac{Beta}{Alpha} = \frac{30 * \frac{251k}{216}}{30 * \frac{k}{216}} = 251\).
Answer: D