Look at this basic funda............
If there are n poeple and each person shakes his hand with all the others the total number of shakehands will be nC2 = n(n-1)/2
In the given problem there are 7 teams with 5 people per team.
So total number of people is 35.
Hence 35C2 shake hands.
But out of these we have to exclude the shakehands among the team members.
Since there are 5 members per team , total number of shakehands among them will be 5C2 = 10.
Since there are 7 teams, total number of shakehands among the team members will be 7x10 = 70.
So the answer must be 35C2- 70
i.e 595-70 = 525.
Averages Accelerated:Guide to solve Averages Quickly(with 10 practice problems)