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From https://brainly.com/question/30733513

Duplicate of https://web2.0calc.com/questions/counting_66045#r1

 

Using combination, the number of ways of placing 8 counters in the square is 12 ways and the number of ways of placing 12 counters in the square is 8 ways

What is the number of ways of placing 8 counters in the square

a) To place 8 counters in the 4 x 4 grid, with exactly two counters in each row, we can first choose the two columns in the first row that will have counters. Using combination, there are {4 C 2} = 6 ways to do this. Then, we choose the two columns in the second row that will have counters, but we need to make sure that these columns are not the same as the ones chosen in the first row. There are only two columns left to choose from, so there are only two ways to do this. Similarly, we choose the two columns in the third row that will have counters, making sure that they are different from the columns chosen in the first two rows. There is only one column left to choose from, so there is only one way to do this. Finally, the columns for the fourth row are uniquely determined. Therefore, the total number of ways to place 8 counters in the grid with exactly two counters in each row is:

6 * 2 = 12

(b) To place 12 counters in the 4 x 4 grid, with exactly three counters in each column, we can start by choosing the three rows that will have counters in the first column. Using combination, there are {4 C3} = 4 ways to do this. Then, we choose the three rows that will have counters in the second column, but we need to make sure that these rows are not the same as the ones chosen for the first column. There are only two rows left to choose from, so there are only two ways to do this. Similarly, we choose the three rows that will have counters in the third column, making sure that they are different from the rows chosen for the first two columns. There is only one row left to choose from, so there is only one way to do this. Finally, the rows for the fourth column are uniquely determined. Therefore, the total number of ways to place 12 counters in the grid with exactly three counters in each column is:

4 * 2 = 8

Thus, there are 12 ways to place 8 counters in the grid with exactly two counters in each row, and 8 ways to place 12 counters in the grid with exactly three counters in each column.

Mar 31, 2023
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We can solve this problem by using casework and counting the number of possibilities for each case.

Case 1: The number has one digit that is equal to 1 and the other digits are equal to 2. There are 8 ways to choose the position of the digit that is equal to 1 (it can be any of the 8 digits). Once we have chosen the position of the digit that is equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^7$ possibilities.

Case 2: The number has two digits that are equal to 1 and the other digits are equal to 2. There are $\binom{8}{2} = 28$ ways to choose the positions of the digits that are equal to 1. Once we have chosen the positions of the digits that are equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^6$ possibilities.

Case 3: The number has three digits that are equal to 1 and the other digits are equal to 2. There are $\binom{8}{3} = 56$ ways to choose the positions of the digits that are equal to 1. Once we have chosen the positions of the digits that are equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^5$ possibilities.

Case 4: The number has four digits that are equal to 1 and the other digits are equal to 2. There are $\binom{8}{4} = 70$ ways to choose the positions of the digits that are equal to 1. Once we have chosen the positions of the digits that are equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^4$ possibilities.

Case 5: The number has five digits that are equal to 1 and the other digits are equal to 2. There are $\binom{8}{5} = 56$ ways to choose the positions of the digits that are equal to 1. Once we have chosen the positions of the digits that are equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^3$ possibilities.

Case 6: The number has six digits that are equal to 1 and the other digits are equal to 2. There are $\binom{8}{6} = 28$ ways to choose the positions of the digits that are equal to 1. Once we have chosen the positions of the digits that are equal to 1, there are 2 possibilities for each of the other digits, for a total of $2^2$ possibilities.

Case 7: The number has seven digits that are equal to 1 and the other digit is equal to 2. There are 8 ways to choose the position of the digit that is equal to 2. Once we have chosen the position of the digit that is equal to 2, there are 2 possibilities for each of the other digits, for a total of $2^7$ possibilities.

Case 8: The number has eight digits that are equal to 2. There is only one possibility in this case.

Thus, the total number of positive integers that satisfy both conditions is:

 

2^7 + 2^6 + 2^5 + 2^4 + 2^3 + 2^2 + 2^7 + 1 = 381.

Mar 31, 2023
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Let $F$ be the foot of the altitude from $H$ to $BC$. Since $H$ lies on altitude $AD$, we have $\angle AHB = 90^\circ$, which means $\angle BHF = 90^\circ - \angle AHB/2 = 56^\circ$. Also, since $H$ lies on altitude $BE$, we have $\angle AHB = 90^\circ$, which means $\angle AHB = 180^\circ - \angle BAC$. Thus, $\angle BAC = 180^\circ - 2\angle BAH = 124^\circ$.

 

Now, we use the fact that the sum of the angles in a triangle is $180^\circ$ to find $\angle HCA$. We have:

\begin{align*}
\angle HCA &= 180^\circ - \angle ACH - \angle AHC \
&= 180^\circ - \angle ACH - (180^\circ - \angle BHA) \
&= \angle BHA - \angle ACH \
&= (180^\circ - \angle BAC) - \angle ACH \
&= 56^\circ - \angle ACH.
\end{align*}

 

Thus, we need to find $\angle ACH$. Since $AF$ is the altitude of triangle $ABH$, we have $\angle ABF = 90^\circ$. Since $\angle BAH = 28^\circ$, we have $\angle BAF = \angle BAH + \angle HAF = 28^\circ + 90^\circ - \angle AHB/2 = 46^\circ$.

Using the fact that the sum of the angles in a triangle is $180^\circ$ in triangle $ABC$, we have:

\begin{align*}
\angle ACH &= 180^\circ - \angle A - \angle CHA \
&= 180^\circ - \angle A - (180^\circ - \angle BHF - \angle BHA) \
&= \angle BHA - \angle A - \angle BHF \
&= (180^\circ - \angle BAC) - \angle A - \angle BHF \
&= 56^\circ - \angle A - \angle BHF.
\end{align*}

 

Thus, we need to find $\angle A$ and $\angle BHF$. Since $AF$ is the altitude of triangle $ABH$, we have $\angle AFB = 90^\circ$, so $\angle BAF + \angle ABF = 46^\circ + 90^\circ = 136^\circ$. Since $\angle BAC = 124^\circ$, we have $\angle BCA = \angle BAC/2 = 62^\circ$. Thus, $\angle A = 180^\circ - \angle BAC - \angle BCA = 180^\circ - 124^\circ - 62^\circ = 14^\circ$.

To find $\angle BHF$, note that $\angle BHF + \angle BHA + \angle AHF = 180^\circ$. Since $\angle BHA = 128^\circ$ and $\angle AHF = 90^\circ - \angle BAF = 44^\circ$, we have $\angle BHF = 180^\circ - \angle BHA - \angle AHF = 8^\circ$.

 

Therefore, $\angle ACH = 56^\circ - \angle A - \angle BHF = 56^\circ - 14^\circ - 8^\circ = 34^\circ$.

Mar 31, 2023
Mar 30, 2023
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Let O be the center of the circumcircle of triangle WXY, and let T be the point where the tangent at X intersects the circumcircle.

Since the tangent at X is perpendicular to the radius OX, we have OT ⊥ XT. Also, since WX is a chord of the circumcircle, we have OT ⊥ WX. Therefore, OT is perpendicular to the line through W that is parallel to the tangent, and so the line through W that is parallel to the tangent passes through the midpoint M of OT.

Since M is the midpoint of OT, we have OM = MT. Also, since OX is a radius of the circumcircle, we have OM = OX. Therefore, MT = OX = 6.

Let P be the point where the line through W that is parallel to the tangent intersects XT. Then, since the line through W is parallel to the tangent, we have ∠XWP = ∠XTX = 90°.

Since ∠XWP = 90°, we have WP ⊥ WX. Also, since MT = 6, we have PT = MT = 6. Therefore, by the Pythagorean Theorem, we have WP = √(XT^2 - PT^2) = √(XT^2 - 36).

Since WP ⊥ WX, we have ∠WPX = 90°. Therefore, by the Pythagorean Theorem, we have WX^2 + XP^2 = WP^2. Substituting WP = √(XT^2 - 36), we get:

6^2 + XP^2 = (XT^2 - 36) XP^2 = XT^2 - 36 - 6^2 XP^2 = XT^2 - 72

Since T is on the circumcircle, we have OT = r, where r is the radius of the circumcircle. Also, since OT ⊥ XT, we have OP = PT = 6. Therefore, by the Pythagorean Theorem, we have OT^2 = OP^2 + PT^2 = 6^2 + 6^2 = 72.

Now, let Q be the point where the line through W that is parallel to the tangent intersects the line through T that is perpendicular to WX. Then, since ∠XWP = 90° and ∠XTW = 90°, we have ∠WXT = ∠XPQ. Therefore, triangles WXT and XPQ are similar, so we have:

XP/XQ = WX/WT XP/(XQ + WX) = WX/OT XP/(XQ + 6) = 6/√72 XP/(XQ + 6) = √2/2

Solving for XP, we get:

XP = (√2/2)(XQ + 6)

Substituting into the previous equation, we get:

(√2/2)(XQ + 6)^2 = XT^2 - 72

Expanding and simplifying, we get:

XQ^2 + 12XQ - 2XT^2 + 144 = 0

Substituting XT = 6√2, we get:

XQ^2 + 12XQ - 72 = 0

Using the quadratic formula, we get:

XQ = (-12 ± √(12^2 + 4(72)))/2 XQ = (-12 ± 6√5)/2

Since XQ > 0, we have:

XQ = -6 + 3√5

Finally, using the Pythagorean Theorem on YTZ, we get

YZ = 8 + 2√5

Mar 30, 2023

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