Question

Two speakers send out sound in phase at a frequency of 779 Hz. When you are the same distance from both speakers you hear a maximum sound. Moving around, you hear essentially no sound when you are 65 cm from one and 85 cm from the other, and again when you are 123 cm from one and 183 cm from the other. What is the speed of sound here?

Answer 1

85-65 = 20 = half a wavelength
183 - 123 = 60 = 1 1/2 wavelengths natch ;)
so wavelength = 40 cm = 0.40 meters
period = 1/779 seconds
so
speed = distance/time = .4 *779 = 311.6 m/s

awful cold there

Answer 2

or high...