菜鸟求教PREP几道题

leijian22

1. For all integers m (m)=3m when m is odd and (m)=0.5m when m is even, which of following is equivalent to (9)*(6)? 81,54,36,27,18.我选81，答案27。
2.For which of following functions f(x)=f(1-x）for all x?  Answer:f(x)= x^2*(1-x)^2   不明白什么意思
3.(DS) What is the tens digit of postive integer r? 1) the tens digit of r/10 is 3. 2)the hundreds digit of 10r is 6

求大家给简单讲解一下。多谢。