Abstract 
In this report, I tried to figure out if  people born after 1980 are more likely to use CITIbike on weekend than people born before 1980.  I applied Z- test to test my hypothesis. The results rejects my Null hypothesis and shows that it is true that  people born after 1980 are more likely to use CITIbike on weekend than people born before 1980 .
Introduction
Bike-sharing systems are becoming increasingly prevalent in urban environments. They provide a low-cost, environmentally-friendly transportation alternative for cities. New York City launched the largest bike-sharing system in North America, Citibike. The system has been a success with ridership approaching 62,000 trips per day (October 2017). Exploring the characteristics of users , especially the travel behavior characteristics based on their ages, is not only very helpful to optimize the management of citi bike system but also make the customize services possible. In this case, analyzing  the different willingness to ride of  different age gourps users on weekend is a good begining. 
Data
The data comes from citibike system data website, I chose two months data: June 2015 and January 2016, to do twice analysis. The data includes: Trip Duration( seconds) , Start Time and Date, Stop Time and Date, Start Station Name, End Station Name, Station ID, Station Lat/Long, Bike ID, User Type (Customer = 24-hour pass or 3-day pass user; Subscriber = Annual Member), Gender (Zero=unknown; 1=male; 2=female), Year of Birth. To complete our analysis, I only need the information of  Start Time and Date and Year of  Birth.  I divided the data into two age groups, which are people born before 1980 and people born after 1980.