3.21 How Many Apps for Your Smartphone? ercise 3.20 describes a study about smartphone users in the US downloading apps for their smart phone. Of the n 355 smartphone users who had downloaded an app, the average number of apps downloaded was 19.7 (a) Give notation for the parameter of interest, and (b) Give notation for the quantity that gives the best (c) What would we have to do to calculate the define the parameter in this context. estimate and give its value. parameter exactly?