A set of football matches is to be organized in a "round-robin" fashion, i.e., every participating team plays a match against every other team once and only once.
If 78 matches are totally played, how many teams participated?
In the opening ceremony of the 2014 FIFA World Cup Brazil, all football teams who participates gathered together. The team captain of each team was handshaking with one another to promote their new act for world peace which was called "A Handshake for Peace!". Each team captain is as polite as the other. How many teams are there if there were a total of 595 handshakes?
A money-conscious student likes to wear a clean shirt every day. He brings his shirts to the laundromat every Monday morning and picks them up exactly one week later. How many shirts does the budget-minded student need to own so that he has a clean shirt to put on every day?
