OPSC 2019 Solved Paper

Sounds of frequencies less than $20\mathit{H}\mathit{z}$ cannot be detected by human ears. Similarly, the sounds of frequencies more than $20,000\mathit{H}\mathit{z}$ cannot be detected by humans.
Hence, the audible range of humans is $20\mathit{H}\mathit{z}$ to $20,000\mathit{H}\mathit{z}$.