Solution: Approximate $3π \approx 9.42$ and $5π \approx 15.71$. Whole numbers between them are 10, 11, 12, 13, 14, 15. Counting these gives $\boxed6$ numbers.A environmental scientist measures the concentration of PM2.5 in a city. If the concentration decreases by 5% every year due to emission controls, starting from 80 µg/m³, what will be the concentration after 5 years? - Crosslake