Elasticity

If the elasticity of demand for coffee is estimated to be -.16, and the quantity demanded is 4 billion pounds per year when the price is $3.60 per pound, how much coffee would be demanded at $2.40 per pound?

How do I solve this question? I don't know how to apply the proper math formula to calculate the answer.

>>1
14 quadrillion megapounds.

WAT.

http://en.wikipedia.org/wiki/Price_elasticity_of_demand#Mathematical_definition

-.16 = -(%change_demand / %change_price)

A change in price from 3.60 to 2.40 is a change of about 41.66666... %.  So, .16*41.666666 = %change_demand = 6.66666...%

%change_demand = change_demand / demand.  6.66666% = (new_demand-old_demand)/old_demand

0.0666666*4b+4b = new_demand
new_demand = 4.26... billion pounds / yr.

Double check my math, I'm no economicisisit.

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