An airport contains 25 terminals which are two on two connected by tunnels. There is exactly 50 main tunnels which can be traversed in the two directions, the others are with single direction. A group of four terminals is called good if of each terminal of the four we can arrive to the 3 others by using only the tunnels connecting them. Find the maximum number of good groups.
it can be solved in the same way as this china 1999 problem:
there are 99 space stations.each pair of space stations is connected by a tunnel.there are 99 two-way main
tunnels and all the other tunnels are strictly one-way tunnels.a group of four space stations is called
connected if one can reach each station in the group from every other station in the group without using
any tunnels other than the 6 tunnels which connect them.determine the maximum number of connected groups.
mlm95 wrote:
it can be solved in the same way as this china 1999 problem:
it's not exactly the same.in this problem the ratio of the mainroads and the stations is $2$,not $1$.