Determine the percent change in optimum recommended fluoride concentration for a water system with annual average maximum daily temperatures of 17.8 to \( 21.4^{\circ} \mathrm{C} \). Hint. The percent change is given by \[ \% \text { change }=\frac{\text { final value - initial value }}{\text { initial value }} \times 100 \% \]

To determine the percent change in the optimum recommended fluoride concentration for a water system with annual average maximum daily temperatures of \( 17.8^{\circ} \mathrm{C} \) to \( 21.4^{\circ} \mathrm{C} \), we first need to know the initial and final values of the fluoride concentration. Assuming you have the initial and final fluoride concentrations based on the temperature ranges, you can use the formula for percent change: \[ \% \text{ change} = \frac{\text{final value} - \text{initial value}}{\text{initial value}} \times 100\% \] Let's denote: - Initial value (fluoride concentration at \( 17.8^{\circ} \mathrm{C} \)) = \( C_1 \) - Final value (fluoride concentration at \( 21.4^{\circ} \mathrm{C} \)) = \( C_2 \) The percent change can then be calculated as: \[ \% \text{ change} = \frac{C_2 - C_1}{C_1} \times 100\% \] If you provide the specific fluoride concentrations for these temperatures, I can help you calculate the percent change.