If 20 beats are produced within one second, which of the following frequencies could possibly be held by two sound waves traveling through a medium along a common path at the same time?

a. 18 hz and 26 hz
b. 47 hz and 55 hz
c. 38 hz and 63 hz
d. 22 hz and 42 hz

D. 22 Hz and 42 Hz

Explanation:

When two waves with different frequency travelling in the same medium meet each other, they produce an interference pattern called beat.The frequency of the beat produced is equivalent to the difference between the individual frequencies of the two waves involved.Therefore; in this case since the frequency of the beat is 20 Hz, that is from 20 beats per second.We need to find a pair from the choices whose frequency difference is 20 Hz.This happens to be choice D. 22 Hz and 42 Hz,  that is 42 Hz - 22 Hz = 20 Hz

Iagree c would be the answer