We expect the demand for coffee to be inelastic for several reasons. It is addictive (well caffinated coffee is), there are few close substitutes (ask any coffee drinker) and the price of a cup of coffee is a relatively small fraction of total expenditure for most consumers. Due to the inelasticity of demand, a reduction in price will be met by a smaller percentage increase in quantity demanded, causing revenues to fall.

We expect the demand for Large-screen TVs to be elastic for several reasons. Such TVs are expensive relative to total expenditure for most consumers, there are plenty of close substitutes (TVs of other sizes and types, keeping your old TV, and getting a life to name a few) thus we expect demand to be very elastic. Reducing the price will lead to a larger percentage increase in quantity demanded, increasing revenues. (Keep in mind that this does not mean profits increase since production costs would go up as well.)
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