其它
A 20\% increase in the price of milk leads to a 10\% decrease in the quantity of cereal purchased. The cross-price elasticity of demand between milk and cereal is 
Overseas Competition->Knowledge Point->Word Problem Modules
This is an application of the cross-price elasticity equation: \% change in QDx/\% change in Py. -0.10/0.2 = -0.5. A negative number means the goods are complements. 