Chapter 4 - Inverse, Exponential, and Logarithmic Functions - 4.4 Evaluation Logarithms and the Change-of-Base Theorem - 4.4 Exercises - Page 458: 68

$2$

Following the definition of Richter scale ratings, compare the results from exercises 66 and 67: $\frac{R_1}{R_2}= \frac{log(\frac{I_1}{I_0})}{log(\frac{I_2}{I_0})}=\frac{9.1}{8.8}$ thus $\frac{I_1}{I_2}=\frac{10^{9.1}}{10^{8.8}}=10^{0.3}\approx2$