某地方有50個縣城,每個縣城都有3條公路通向別的縣城,這些縣城之間共有多少條公路?(請詳細解答)

熱心網友

設每個縣城為一點,每條公路為一條線. 因為每個點有3條線連接(50乘3),那么這樣每兩個點之間就重復了一條線(那么就要除2).所以50乘3除2=75. 答:有75條公路

熱心網友

8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8--8-----||\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |.....| 8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8-8--8 ....| | .....................................................| |______________________________________________________|26條公路.