Answer : 4 beats per second.
Explanation :
The two components of the frequencies are given as :


The beating is the phenomenon of the interference of sound resulting in the production of alternatively soft or loud sound. The difference in the frequencies of the two components is called beat frequency.
Mathematically, it is given by :



So, if the frequencies of two component waves are 24 Hz an 20 Hz, they should produce 4 beats per second.