Question

if a source of sound produces 500 compressions and 500 rarefaction in air in 25 seconds find the frequency of sound produced

Answer 1

According to question

Number of Compressions = m = 500

And

Number of rarefactipns  = n = 500
Also
Frequency F = 25 Sec

Thus
Frequency produced = m + n / 25
                                   = 1000 / 25
                                   = 40

Answer 2

Frequency=500/25

= 20

It is correct answer . You should not add 500+500 . U should take only 500 and sec=25. So 500/25

= 20

Hope it helps .