Answer : Reaction time is usually a measure of the quickness an organism response to some sort of external stimulus. Reflexes and reactions, which may appear to be similar, are quite different. Reflexes are observed to be involuntary, which is used to protect the body, and are faster than a reaction.
So, in this case, when the easy simple task was given brain required less time to respond to those questions as the response time didn't included interpretation of the sound. Faster reaction response time are mostly seen in easy tasks which does not includes complex thinking by the brain.