how to hosting multiple Nodejs applications with nginx

I understand that multiple node.js can be run on one server using Nginx. I've got Nginx setup and running on a Ubuntu server. I have two node js applications :

    127.0.0.1:3001 and 
    127.0.0.1:3002

. I want to access the different application with different url. For example, if I want access

    127.0.0.1:3001

, I would use url:

 http://121.42.20.100/

. And if want access the application of

    127.0.0.1:3002

, I would use url:

 http://121.42.20.100/admin 

the default file on the folder sites-available follows :

    server {
            #listen   80; ## listen for ipv4; this line is default and implied
            #listen   [::]:80 default ipv6only=on; ## listen for ipv6

            root /usr/share/nginx/www;
            index index.html index.htm;

            # Make site accessible from `    http://localhost/`
            server_name 0.0.0.0;

            location / {

                   proxy_pass `    http://127.0.0.1:3001`;

            }

            location /admin/ {
                    proxy_pass `    http://127.0.0.1:3002`;
            }
    }

When I access url like

http://121.42.29.100/

, it works that get response from

 
    127.0.0.1:3001

. However, when I access url like

http://121.42.29.100/admin

, it does not work that it shows error of "Cannot GET /admin/". How can I configure the nginx to get it work?