n=20×(3000÷500)1/2=20×2.45=49(个)答:份样数是49个
n=20×(2000÷500)1/2=40(个)答:份样数是40个
n=60×(30×50/1000)1/2=60×1.22=73.2≈74(个)答:份样数是74个