足球隊(duì):??$\frac {1}{5}$??=??$\frac {4}{20}$??
籃球隊(duì):??$\frac {1}{4}$??=??$\frac {5}{20}$??
乒乓球隊(duì):??$\frac {3}{10}$??=??$\frac {6}{20}$??
羽毛球隊(duì):1- ??$\frac {1}{5}$??-??$\frac {1}{4}$??-??$\frac {3}{10}$??=??$\frac {1}{4}$?? ??$\frac {1}{4}$??=??$\frac {5}{20}$??
因?yàn)???$\frac {4}{20}$?? < ??$\frac {5}{20}$?? < ??$\frac {6}{20}$??,即 ??$\frac {1}{5}$?? < ??$\frac {1}{4}$?? < ??$\frac {3}{10}$??
答:乒乓球隊(duì)的人數(shù)最多。