Calculatin aRoute Summarization !!!!

lets look at the following four networks :

172.20.0.0/16                                                                                           
172.21.0.0/16
172.22.0.0/16                                                                                                     
172.23.0.0/16

1st Step you should convert all octet to binary :

  128    64    32   16   8    4   2   1

172.20.0.0          1 0 1 0 1 1 0 0 . 0 0 0 1 0 1 0 0 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0

172.21.0.0          1 0 1 0 1 1 0 0 . 0 0 0 1 0 1 0 1 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0

172.22.0.0          1 0 1 0 1 1 0 0 . 0 0 0 0 0 1 1 0 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0

172.23.0.0          1 0 1 0 1 1 0 0 . 0 0 0 0 0 1 1 1 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0

                                                            

count the number of left-most matching bits to determine the mask 14 matching bits its mean by CIDR /14  or by Subnet mask 255.252.0.0

so about 

172.20.0.0/16                                         
172.21.0.0/16
172.22.0.0/16
172.23.0.0/16

can be summarized into the single network address and prefix 172.20.0.0/14