The correct answer is: "I would recommend her not to increase the price, because with an elastic demand function this will cause a great decrease in the quantity demanded by consumers".
The demand function represents the quantity of a certain good or service that consumers are willing to purchase in the market at different price levels. The law of demand states that there is an inverse relationship between price and quantity demanded (ceteris paribus, hence, given that the rest remains equal). Therefore, when the price charged decreases, the amount that consumers are willing to purchase increases.
In turn, the elasticity of the demand function measures the sensitiveness of the quantity demanded by consumers when there is a certain price change. If the demand function is elastic it means that a price variation would generate an even larger variation (in the inverse direction of course!) in the quantity demanded. This is the case of the lemonade stand therefore the girl should not increase prices because this will not help her to reach her objective quicker, as she would loss a greater proportion of units sold than the size of the price increase that would have allowed her to earn more per unit.
