Sound from a small loudspeaker L reaches a point P by two paths which differ in length by 1.2m. When the frequency of the sound is gradually increased, the resultant intensity at P goes through a series of maxima and minima. A maximum occurs when the frequency is 1000 Hz and the next maximum occurs at 1200 Hz. What is the speed of sound in the medium between L and P?
A 200
B 240
C 480
D 1200
E 1400
Then 1.2 =1/4 of
see attached doc
