Your sonic range finder measures the distance to a nearby building at 20m. The range finder is calibrated for sound traveling 343 m/s, but on this very cold day the speed of sound is only 309 m/s. How far away is the building?

Answer 1

distance out and back = 2d
distance = rate * time
40 = 309 t
t = 40/309 (the finder actually measured this time)

2*real distance = 343 (40/309)

real distance = 343 (20/309)