One important use of logarithms is to solve exponential equations. In this chapter, we will also consider logarithmic functions as models in their own right. Additionally, we will look further at the number $e\text{,}$ which is the most useful base for many scientific applications.
 Time elapsed Percent remembered $20$ minutes $58.2\%$ $1$ hour $44.2\%$ $9$ hours $35.8\%$ $1$ day $33.7\%$ $2$ days $27.8\%$ $6$ days $25.4\%$ $31$ days $21.1\%$