Two Motors in a Factory Are Running at Slightly Different

Multiple Choice

Two motors in a factory are running at slightly different rates.One runs at 825 rpm and the other at 786 rpm.You hear the sound intensity increase and then decrease periodically due to wave interference.How long does it take between successive instances of the sound intensity increasing?

A) 1.54 s
B) 1.43 s
C) 1.66 s
D) 1.79 s