The sound wave produced by a trumpet has a
frequency of 440 hertz. what is the distance
between successive compressions in this sound
wave as it travels through air at stp?
(1) 1.5 × 10^–6 m (3) 1.3 m
(2) 0.75 m (4) 6.8 × 10^5 m

             Wavelength = (speed) / (frequency)

so in order to answer this question, we need the speed of sound.

Without using my precious time to go look it up, I'm guessing that
the speed of sound at STP is roughly  343 m/s .

If that estimate is accurate, then

         Wavelength = (343 m/s) / (440 /s)  =  0.78 meter .

Choice-#2 is much closer to this result than any of the others,
so choice-2 must be it.

Actually, we can 'reverse engineer' Choice-#2 and find the number
it uses for the speed of sound.

       Speed = (wavelength) x (frequency)

                   = (0.75 m) x (440 /s)  =  330 m/s .

The author of the question used  330 m/s  for the speed of sound.

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