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This is Giancoli Answers with Mr. Dychko. Wave speed is frequency times wavelength when we divide both sides by f we can solve for λ the wavelength is the speed of sound divided by its frequency. So, the wavelength at 20 hertz is 343 meters per second speed of sound, divided by 20 hertz which is about 17 meters. And then at 20,000 hertz or 20 kilohertz the wavelengths will be 343 meters per second divided by 20,000 which is about 1.7 centimeters when you convert those then, you know, it's 0.017 meters but 1.7 centimeters is easier to think about. And then in part b the wavelength for an 18 mega hertz sound would be 343 meters per second divided by 18 times 10 to the 6, because that's the exponent for 10 when you have the prefix in mega 10 to the 6 and then you have 1.9 times 10 to the minus 5 meters.