AnkurGMAT20
Bunuel, I'm having difficulty understanding this question and the solution. Can you please help?
Last year a company produced millions of widgets each week. Last year the ratio of the number of defective widgets to the number of widgets produced was \(\frac{1}{4}\) for the first week, \(\frac{1}{8}\) for the second week, \(\frac{1}{16}\) for the third week, and so on for 19 weeks, where the ratio for each week after the first week was half of the ratio for the preceding week. If last year the ratio of the number of defective widgets to the number of widgets produced was \(d\) for the 19th week, then \(d\) satisfies which of the following inequalities? A. \(d < \frac{1}{1,000,000}\)
B. \( \frac{1}{1,000,000} \leq d < \frac{1}{100,000} \)
C. \( \frac{1}{100,000} \leq d < \frac{1}{10,000} \)
D. \( \frac{1}{10,000} \leq d < \frac{1}{1,000} \)
E. \(d \geq \frac{1}{1,000}\)
We are given that the ratio of the number of defective widgets to the number of widgets produced halves each week.
- The ratio for 1st week was \(\frac{1}{4} = \frac{1}{2^2}\);
- The ratio for 2nd week was \(\frac{1}{8} = \frac{1}{2^3}\);
- The ratio for 3rd week was \(\frac{1}{16} = \frac{1}{2^4}\);
and so on.
Hence, the ratio for the nth week would be \(\frac{1}{2^{n+1}}\), making the ratio for the 19th week equal to \(\frac{1}{2^{20}}\).
Essentially now we need to evaluate the value \(\frac{1}{2^{20}}\) to answer the question. Since \(2^{20}=(2^{10})^2=1,024^2 > (1,000^2=1,000,000)\), then \(\frac{1}{2^{20}}< \frac{1}{1,000,000}\).
Answer: A.
Hope it helps.