Math Is Fun Forum

Why?
If so , I should use partial sum n , then prove n-->infinity converge?

Oh , right , I remember there's an expansion of it.

More direct way of thinking

Is it because all decimal number

I have an idea , but I haven't work out the whole method
if you draw  the graph of 

they will be symmetric , I think applying geometric method will help , still don't know yet...

Is this some Cryptographical decoding games?

To 31
  there are 33 numbers which are the multiple of 3 , then the probability of chosing one from 1-100 will be 33/100  , if u chose two number which are not the multiple of 3 , then the probability is (67/100)^2 , then the probability we want is  1- (67/100)^2

To 32 ,
  P(A)=x , P(B)=y
xy= 1/6 ,  (1-x)(1-y)=1/3
y=5/7 ,x= 7/30

If x is positive , as u can see , it will be  (-1) + 1 + (-1)+1 + (-1) not equal to 0  , and because there are 5 pair , so one of those pairs must be 0 ,  therefore 5 solutions. x must great than -9

Oh yah , wrong order ha!