Not sure if the equation is

or








On the other side of the equation, we'd get

Then

- If it's the second one instead, you can use the same strategy as above:


(Note that this step assume
)



Then we get

Answer:
9.11*10^-4 %
Step-by-step explanation:
To find the probability, you simply need to find the possible outcomes that allows no rooks to be in danger, and the possible amount of ways to place the rooks.
For the first outcome, you start by putting 1 rook in the first columns, you have 8 possible rows to do this. The next rook in the next column will only have 7 possible rows, as you have to exclude the one where the previous rook is located. The next rook, 6 possibilities, the next 5, and so on. So we conclude that the total amount of ways so that none of the rooks can capture any of the other rooks is 8*7*6*5*4*3*2*1 = 8! = 40320
In order to find the total amount of ways to place the rooks, you can just use a combinatoric:
![\left[\begin{array}{ccc}64\\8\end{array}\right]= \frac{64!}{8!(64-8)!} = 4.43*10^9](https://tex.z-dn.net/?f=%5Cleft%5B%5Cbegin%7Barray%7D%7Bccc%7D64%5C%5C8%5Cend%7Barray%7D%5Cright%5D%3D%20%5Cfrac%7B64%21%7D%7B8%21%2864-8%29%21%7D%20%3D%204.43%2A10%5E9)
Then:
P = 
Answer:
c
Step-by-step explanation:
Answer:
11
Step-by-step explanation:
LOL
Well, 20% is equivalent to (1/5). So, you'd put 50 in the numerator and 5 in the denominator. (50/5) is equal to 10. Then you'd take that value and subtract it from your original value. [ 50 - 10 = 40 ]. 40 Students were at school that day.