如果正方形的边长为acm,它的面积与长96cm,宽为12cm的矩形的面积相等.求a的值.
解;设正方形的边长为acm,
a•a=96×12
a=242
正方形的边长242cm.
某乡5000户约2万人口,欲抽其1/5人口进行某病调查。随机抽取第1户,随后每隔5户抽取1户,抽到户的每个成员均进行调查。这种抽样方法称为()
A.分层抽样
B.系统抽样
C.整群抽样
D.简单抽样
E.多级抽样
It’s said that the food supplies in that flood-stricken area have __________ and what is worse, the patience of the poor people there is _______.
A.run out; using up
B.been run out; used up
C.been used up; running out
D.used up; being run out