【解析】由条件=,知,数列{,}是等比数列,则其公比满足q=92=39=万因此a3=am9=335.【解析】由频率分布直方图可知,月用水量在[0,0.5)的频率为0.08×0.5=0.04.同理,在[0.5,1),[1.5,2),[2,2.5),[3,3.5),[3.5,4),[4,4.5]等组的频率分别为0.08,0.21,0.25,0.06,0.04,0.02.由1-(0.04+0.08+0.21+0.25+0.06+0.04+0.02)=2×0.5×a,解得a=0.30,设中位数为x吨.因为前5组的频率之和为0.04+0.08+0.15+0.21+0.25=0.73>0.5,而前4组的频率之和为0.04+0.08+0.15+0.21=0.48<0.5,所以2≤x<2.5.由0.50×(x2)=0.5-0.48,解得x=2.04
6.【解析】k=0时,s=4:k=1时,s=-4-4=-8:k=2时,s=28+4=-20k+1=323时此时退出循环,输出的=~30