beckhamine wrote:
I think the answer is not 1/2
lets call i the indice number of rows and j the indice number for columns.
As we are looking at the odd numbers, (i,j) are in [1,3,5,7,9].
Now the probability of getting a zero is the probability of having i>= j.
so the number of possibilities to get i>= j when chosing a couple of numbers is 5+4+3+2+1=15.
(if j=1, you have 5 choices, if j=3, you have 4 choices ...)
The number of possibilities is 5*5=25.
So the probability to get a zero is 15/25 = 3/5
Yes! I think you are correct - also, nice explanation!
For those who did not get it, here is the diagram:
Attachment:
11.JPG [ 38.33 KiB | Viewed 3827 times ]
The shaded boxes are those that belong to odd rows and odd columns
There are 25 such boxes and the number of zeroes is 15
Hence, 15/25 = 3/5 should be the correct answer