A coffee company is interested in the coffee drinking habits of people
in India.  What is the problem in asking subjects: "How many cups of
coffee have you consumed in the pat 30 days?"  What subjects would be
the most likely to provide an accuate description? How could this
question be modified to provide more accurate data?

Perhaps they won't be able to remember how many cups of coffee they
had for the past 30 days.  It would be easier for them to answer if
you asked them how many cups they have had today.