Official Solution:The value of \(\frac{7^{5} - 10^{20}}{5^{20} - 3^{5}}\) is A. less than \(-10^6\)
B. greater than \(-10^6\) and less than \(-10^4\)
C. greater than \(-10^4\) and less than \(-10^2\)
D. greater than \(-10^2\) and less than \(0\)
E. greater than \(0\)
Expressions both in the numerator and denominator are quite ugly and do not factor nicely. However, looking at the answer options, we see that they are well spread, which should be a hint that we should
approximate.
Observe that \(10^{20}\) is a
significantly larger number than \(7^{5}\), which makes \(7^{5}\) negligible in comparison. Likewise, \(5^{20}\) is
much, much larger than \(3^{5}\), making \(3^{5}\) also negligible. Therefore:
\(\frac{7^{5} - 10^{20}}{5^{20} - 3^{5}} \approx \)
\(\approx\frac{-10^{20}}{5^{20}} = \)
\(=\frac{-2^{20}5^{20}}{5^{20}} = \)
\(=-2^{20} = \)
\(=-2^{10} 2^{10} \approx \)
\(\approx- 1,024*1,024\)
The above expression will be less than -1,000,000, which is \(-10^6\).
Answer: A