2.7+3.1+2.9+3.2.
2.7+3.1+2.9+3.2,
=2.7+(3.1+2.9)+3.2,
=2.7+6+3.2,
=11.9.
下列运算正确的是 [ ]
A.a2+a3=a5
B.a2·a3=a5
C.(a2)3=a5
D.a10÷a2=a5
有人研究授乳与乳腺癌的关系,回顾性的调查如下
经计算其OR为()
A.208×66/192×50
B.192×50/208×66
C.208/(208+50)
D.208/400-50/116
E.资料不全,无法计算