Using the formula , calculate the demand elasticities for the following examples: Ice CreamThe price of ice cream increased from $3.00 a litre to $3.25 a litre. This change in price caused demand to drop from 4000 litres a day to 3400 litres a day. RollerbladesThe price of rollerblades decreased from $375.00 to $325.00. This change in price caused demand to increase from 20 sales a day to 32 sales a day.