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 #1
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Here is part a:

 

There are two ways to approach this problem:

 

Method 1: Analyzing the Cube's Layers

 

Outermost Layer:

 

Each face of the large cube contributes a single layer of smaller cubes to the final set.

 

Since each face is painted black, the outermost layer of smaller cubes will all have one black face.

 

There are 6 faces, and each face contributes a layer of 3 * 3 = 9 cubes.

 

So, the outermost layer contributes a total of 6 faces * 9 cubes/face = 54 cubes with one black face.

 

Inner Cubes:

 

The inner cubes are completely enclosed by other cubes and won't have any black faces.

 

Method 2: Identifying Specific Locations

 

Cubes on Edges:

 

Cubes on the edges of the larger cube will have exactly two black faces (one from each adjacent larger face).

 

There are 12 edges (4 on each length), and each edge contributes 2 cubes.

 

So, the edges contribute a total of 12 edges * 2 cubes/edge = 24 cubes with two black faces.

 

Cubes on Corners:

 

Cubes on the corners of the larger cube will have exactly three black faces (one from each adjacent larger face).

 

There are 8 corners (one at each vertex), and each corner contributes 1 cube.

 

So, the corners contribute a total of 8 corners * 1 cube/corner = 8 cubes with three black faces.

 

Center Cube:

 

The cube in the exact center of the larger cube won't have any black faces.

 

Total with One Black Face:

 

Since none of the inner cubes and only the outermost layer has cubes with one black face, we can subtract the cubes with multiple black faces from the total number of cubes on the faces (54) to find the ones with exactly one black face.

 

Total cubes on faces = 6 faces * 3 cubes/face * 3 cubes/face = 54 cubes Total cubes with multiple black faces = 24 cubes (edges) + 8 cubes (corners) = 32 cubes

 

Therefore, there are 54 cubes (total on faces) - 32 cubes (multiple black faces) = 22 cubes with exactly one black face.

 

Answer:

 

Both methods lead to the same answer: there are 22 cubes with exactly one black face.

Apr 17, 2024
 #1
avatar+179 
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There seems to be an error in the provided code. The result shows 0, which is incorrect.

Let's solve this problem using a dynamic programming approach.

We can define a 2D table dp where dp[i][j] represents the number of ways to distribute i stickers among j friends.

Base Case: If there are no stickers (i = 0), there's only one way (no distribution) for any number of friends (j). So, initialize dp[0][j] to 1 for all j.

Inductive Case: For a given number of stickers (i) and friends (j), we have two options:

Give the current friend a sticker (option 1). In this case, we use the number of ways to distribute the remaining stickers (i - 1) among the remaining friends (j - 1). This is captured by dp[i - 1][j - 1].

Don't give the current friend a sticker (option 2). In this case, we use the number of ways to distribute the same number of stickers (i) among the same number of friends (j). This is captured by dp[i][j - 1].

The total number of ways for dp[i][j] is the sum of these two options.

Implementation:

Python

def distribute_stickers(stickers, friends): """ This function calculates the number of ways to distribute a given number of identical stickers among a specified number of friends, where some friends may not receive any stickers. Args: stickers (int): The total number of identical stickers. friends (int): The number of friends. Returns: int: The number of ways to distribute the stickers. """ # Use dynamic programming to solve the problem. # dp[i][j] represents the number of ways to distribute i stickers among j friends. dp = [[0 for _ in range(friends + 1)] for _ in range(stickers + 1)] # Base case: If there are no stickers, there's only one way (no distribution). for friend in range(friends + 1): dp[0][friend] = 1 # Iterate through the number of stickers and friends. for sticker in range(1, stickers + 1): for friend in range(1, friends + 1): # Option 1: Give the current friend a sticker. dp[sticker][friend] += dp[sticker - 1][friend - 1] # Option 2: Don't give the current friend a sticker. dp[sticker][friend] += dp[sticker][friend - 1] # The final answer is the number of ways to distribute all stickers (stickers) among all friends (friends). return dp[stickers][friends] # Example usage: Find the number of ways to distribute 12 stickers among 8 friends. number_of_ways = distribute_stickers(12, 8) print(number_of_ways)

Use code with caution.

content_copy

Explanation:

The code iterates through the number of stickers and friends, filling the dp table. For each cell dp[i][j], it calculates the sum of the two options mentioned above and stores it in the cell. Finally, dp[stickers][friends] gives us the total number of ways to distribute 12 stickers among 8 friends.

This approach correctly considers the scenario where some friends might not receive stickers.

Apr 17, 2024
 #1
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Analyze the Area:

 

We need to find the area of the shaded region visible after placing the circles. There are two approaches:

 

Method 1: Finding the Unshaded Area

 

Calculate the total area of the grid (5 squares * 5 squares * 2 cm * 2 cm) = 100 cm².

 

Calculate the total area of each circle (pi * radius^2). Since the radius is half the side length of a square (1 cm), the area of each circle is pi * (1 cm)^2 = pi cm².

 

Calculate the total area covered by the circles (5 circles * pi cm² per circle) = 5 pi cm².

 

Subtract the total area covered by the circles from the total area of the grid to find the visible shaded area.

 

Method 2: Finding the Shaded Area Remaining

 

Identify the area of each shaded square that remains visible after placing a circle. In each case, a quarter circle is removed from the square.

 

Calculate the area of a quarter circle (pi * radius^2) / 4 = (pi * 1 cm²) / 4 = pi/4 cm².

 

Calculate the remaining shaded area of each square with a circle (area of square - area of removed quarter circle) = (4 cm² - pi/4 cm²).

 

Multiply the remaining shaded area per square by the number of squares with circles (4 squares) to find the total visible shaded area.

 

Solve Using Either Method:

 

Method 1:

 

Total area of grid = 100 cm²

 

Total area of circles = 5 pi cm²

 

Visible shaded area = 100 cm² - 5 pi cm² = A - 5 pi cm²

 

Method 2:

 

Remaining shaded area per square = 4 cm² - pi/4 cm²

 

Total visible shaded area = 4 squares * (4 cm² - pi/4 cm²) = 16 cm² - 4 pi cm² = A - 4 pi cm²

 

Since both methods lead to the same form for the visible shaded area (A - B pi cm²), we can equate the coefficients of pi:

 

-5 pi (from Method 1) = -4 pi (from Method 2)

 

This equation holds true, confirming that both methods lead to the correct form.

 

Find A + B:

 

Since the coefficient of pi is negative in both methods, B represents the absolute value of the pi term.

 

Looking at the equation -5 pi = -4 pi, we see that B = 5 (the absolute value of -4 pi).

 

Therefore, A + B = A + 5.

 

Finding A:

 

Since the visible shaded area is a combination of whole squares and quarter circles removed from squares, the value of A should represent the area of whole squares remaining visible. From the grid, we can see there are 9 whole squares remaining visible.

 

Therefore, A = 9 * (area of one square) = 9 * 4 cm² = 36 cm².

 

Final Answer:

 

A + B = 36 + 5 = 41.

 

So the value of A + B is 41.

Apr 17, 2024
 #1
avatar+179 
0

We can solve this problem by using the formula for the nth term of a geometric sequence and the information given about the first few terms.

 

Relate Terms with Formula:

 

Let r be the common ratio of the geometric sequence. We know the first term (a1) but not its specific value.

 

We are given that the second term (a2) is three more than the first term, so a2 = a1 + 3.

 

Similarly, the third term (a3) is seven more than the second term, so a3 = a2 + 7.

 

The general formula for the nth term of a geometric sequence is:

 

an = a1 * r^(n-1)

 

Find the Common Ratio (r):

 

We can use the information about the second and first terms to find the common ratio. We know that a2 = a1 * r:

 

a2 = a1 + 3 (given) a1 * r = a1 + 3

 

Since a1 is not zero, we can divide both sides by a1 to isolate r:

 

r = 1 + 3/a1

 

Find a3 using the formula and r:

 

We can now use the formula for a3 and the value we found for r:

 

a3 = a1 * r^2 = a1 * (1 + 3/a1)^2

 

We are also given that a3 = a2 + 7:

 

a1 * (1 + 3/a1)^2 = a1 + 3 + 7

 

Simplify and Solve for a1:

 

Expanding the square in the first term:

 

a1 + 6/a1 + 9/a1^2 = a1 + 10

 

Combining like terms:

 

6/a1 + 9/a1^2 = 10

 

Taking a common denominator of a1^2:

 

6a1 + 9 = 10a1^2

 

Rearranging the equation:

 

10a1^2 - 6a1 - 9 = 0

 

Factoring the expression:

 

(2a1 + 3)(5a1 - 3) = 0

 

Therefore, a1 = -3/2 or a1 = 3/5.

 

Find a4 based on a1 and r:

 

Since a negative value for a1 wouldn't make sense in a geometric sequence with positive terms, we know a1 = 3/5. Now we can find the common ratio (r):

 

r = 1 + 3/a1 = 1 + 3 / (3/5) = 8/3

 

Finally, let's find the value of a4 using the formula and the values of a1 and r:

 

a4 = a1 * r^3 = (3/5) * (8/3)^3 = (3/5) * 512/27

 

Therefore, the value of a4 is 1024/135, expressed as a common fraction.

Apr 17, 2024