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Y_Kistochka [10]
3 years ago
5

Eights rooks are placed randomly on a chess board. What is the probability that none of the rooks can capture any of the other r

ooks? Translation for those who are not familiar with chess: pick 8 unit squares at random from an 8x8 square grid. What is the probability that no two chosen squares share a row or a column?
Mathematics
1 answer:
erastova [34]3 years ago
7 0

Answer:

The probability is \frac{56!}{64!}

Step-by-step explanation:

We can divide the amount of favourable cases by the total amount of cases.

The total amount of cases is the total amount of ways to put 8 rooks on a chessboard. Since a chessboard has 64 squares, this number is the combinatorial number of 64 with 8, 64 \choose 8 .

For a favourable case, you need one rook on each column, and for each column the correspondent rook should be in a diferent row than the rest of the rooks. A favourable case can be represented by a bijective function  f : A \rightarrow A , with A = {1,2,3,4,5,6,7,8}. f(i) = j represents that the rook located in the column i is located in the row j.

Thus, the total of favourable cases is equal to the total amount of bijective functions between a set of 8 elements. This amount is 8!, because we have 8 possibilities for the first column, 7 for the second one, 6 on the third one, and so on.

We can conclude that the probability for 8 rooks not being able to capture themselves is

\frac{8!}{64 \choose 8} = \frac{8!}{\frac{64!}{8!56!}} = \frac{56!}{64!}

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Write an equation in slope-intercept form for the following line:<br><br> (-14,1) and (13,-2)
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Answer:

\large \boxed{y =  -  \frac{1}{9} x -  \frac{5}{9} }

Step-by-step explanation:

In order to find an equation of a line with two given ordered pairs. We have to find a slope first which we can do by using the formula below.

\large \boxed{m =  \frac{y_2 - y_1}{x_2 - x_1} }

m-term is defined as slope in y = mx+b form which is slope-intercept form.

Now we substitute these ordered pairs (x, y) in the formula.

\large{m =  \frac{1 - ( - 2)}{ -14 - 13} } \\  \large{m =  \frac{1 + 2}{ - 27} } \\  \large{m =  \frac{3}{ - 27}  =  -  \frac{1}{9} }

After we calculate for slope, we substitute m-value in slope-intercept form. The slope-intercept form is

\large \boxed{y = mx + b}

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\large{y =  -  \frac{1}{9} x  + b}

We are not done yet because we need to find the b-term which is our y-intercept. (Note that m-term is slope while b-term is y-intercept)

We can find the y-intercept by substituting either (-14,1) or (13,-2) in the equation. I will be using (13,-2) to substitute in the equation.

\large{y = -  \frac{1}{9} x + b} \\  \large{ - 2 =  -  \frac{1}{9} (13) + b} \\  \large{ - 2 =  -  \frac{13}{9}  + b} \\  \large{ - 2 +  \frac{13}{9}  = b} \\  \large{ -  \frac{5}{9}  = b}

Finally, we know b-value. Then we substitute it in our equation.

\large{y =  -  \frac{1}{9} x + b} \\  \large{y =  -  \frac{1}{9} x -  \frac{5}{9} }

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