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 #1
avatar+1133 
0

We can solve this problem by considering two cases:

 

Case 1: One family has siblings in each row

 

There are 3 families (let's call them A, B, and C). In this case, we need to place one child from each family in each row. There are 3 choices for the first seat in the first row (child from any family).

 

Once the first seat is filled, there are 2 choices left for the second seat (child from one of the remaining families). The third seat is automatically filled by the remaining child.

 

Similarly, for the second row, there are again 3 choices for the first seat, and so on. Therefore, the number of arrangements for this case is:

 

Arrangements (Case 1) = 3 * 2 * 3 * 2 = 36

 

Case 2: Two families have siblings in one row

 

There are again 3 choices for which family will have siblings in the same row (A, B, or C). Without loss of generality, let's say family A has siblings in the same row.

 

There are now 2 choices for which child of family A sits in the first seat of the first row. The other child of family A must sit in the second seat.

 

The remaining child from family B can sit in the third seat. Now, for the second row, there are 2 choices for the first seat (child from either family B or C). Following the same logic as before, the number of arrangements for this case is:

 

Arrangements (Case 2) = 3 * 2 * 1 * 2 * 2 = 24

 

Total Arrangements

 

To get the total number of arrangements, we add the number of arrangements from both cases:

 

Total Arrangements = Arrangements (Case 1) + Arrangements (Case 2)

 

Total Arrangements = 36 + 24

 

Total Arrangements = 60​

Apr 21, 2024
Apr 20, 2024
 #1
avatar+1036 
-1

Here's another way to solve this problem, focusing on proportionality within the parallelogram:

 

Proportions in Similar Triangles:

 

Since ABCD is a parallelogram, lines AD and BC are parallel. When line DE intersects line BC at point F, it creates two transversal lines. Because of this, corresponding angles on alternate sides of DE are congruent (alternate interior angles)

 

Therefore, triangles EAD and EBF are similar by Angle-Angle Similarity (AA).

 

Since the triangles are similar, the ratio of their areas is equal to the square of the ratio of their corresponding side lengths:

 

Area(EBF) / Area(EAD) = (length(BF) / length(AD))^2

 

Given Information:

 

We are given that the area of triangle EBF is 4 and the area of triangle EAD is 9. Plugging these values into the equation:

 

4 / 9 = (length(BF) / length(AD))^2

 

Proportionality in a Parallelogram:

 

In a parallelogram, opposite sides have the same length. Therefore, length(BF) = length(AE) and length(AD) = length(BC). Substituting these equalities into the equation from step 2:

 

4 / 9 = (length(AE) / length(BC))^2

 

Area of Parallelogram:

 

The area of a parallelogram is equal to the base times the height. Since AD is parallel to BC, the height of parallelogram ABCD is the same as the height of triangle EAD (considering side AE as the base). We can express this using proportionality:

 

Area(ABCD) ∝ length(BC) * height(EAD)

 

From step 3, we know the ratio between the base of triangle EAD (which is also a base of the parallelogram) and side BC of the parallelogram:

length(AE) / length(BC) = √(4/9) (taking the square root of both sides)

 

Combining Proportions:

 

Since the area of the parallelogram is proportional to the product of its base and height, and we know the ratio between the base and a side of the parallelogram, we can combine these proportions:

 

Area(ABCD) ∝ (√(4/9)) * height(EAD)

 

Note: We don't need to find the actual height of triangle EAD since it cancels out when solving for the relative area of the parallelogram.

 

Relative Area of Parallelogram:

 

Since the area of triangle EAD is a constant value (9) and the other factor in the proportion is a constant resulting from the given information, the area of parallelogram ABCD is also proportional to a constant value.

 

Therefore, relative to the area of triangle EAD, the area of parallelogram ABCD is:

 

Area(ABCD) ∝ √(4/9) * Area(EAD) = √(4/9) * 9 = 4

 

Scaling to Actual Area:

 

While the previous step gives us the relative area compared to triangle EAD, we can find the actual area by considering that the area of triangle EBF is given as 4.

 

Since triangles EAD and EBF are similar, the ratio of their areas is the square of the ratio of their corresponding side lengths (as established in step 1). Therefore, the area of triangle EAD is 4 times the area of triangle EBF:

 

Area(EAD) = 4 * Area(EBF) = 4 * 4 = 16

 

Now, we can use the relative area we found in step 6 to solve for the actual area of the parallelogram:

 

Area(ABCD) = √(4/9) * Area(EAD) = √(4/9) * 16

 

Area(ABCD) = 4 * 4 = 16​.

Apr 20, 2024
Apr 19, 2024
 #1
avatar+1588 
-1

Identify Similar Triangles:

 

Since ABCD is a parallelogram, lines AD and BC are parallel. When line DE intersects line BC at point F, it creates two transversal lines (AD and BC).

 

Because of this, corresponding angles on alternate sides of DE are congruent (alternate interior angles). Therefore, triangles EAD and EBF are similar by Angle-Angle Similarity (AA).

 

Ratio of Areas:

 

Since triangles EAD and EBF are similar, the ratio of their areas is equal to the square of the ratio of their corresponding side lengths.

 

e are given that the area of triangle EBF is 4 and the area of triangle EAD is 9. Let the ratio between a corresponding side length in EBF and the corresponding side length in EAD be k. Therefore:

 

Area(EBF) / Area(EAD) = k^2

 

4 / 9 = k^2

 

k = ± (2/3) (We can take the positive or negative value of k since it represents a ratio of side lengths, which can be positive or negative depending on direction.)

 

Relating Side Lengths in Similar Triangles:

 

Since k represents the ratio between corresponding side lengths in the similar triangles, we can express the lengths of sides BE and AE in terms of k:

BE = k * AE (BE corresponds to a side in EBF and AE corresponds to a side in EAD)

 

Area of Triangle EBF:

 

We are given that the area of triangle EBF is 4. The area of a triangle can be calculated as:

 

Area = (base * height) / 2

 

Since BE is the base of triangle EBF and DF is the height with respect to that base (DF is perpendicular to BE), we can set up an equation:

 

4 = (BE * DF) / 2

 

8 = BE * DF (multiply both sides by 2)

 

Relating Heights in Similar Triangles:

 

Since triangles EAD and EBF are similar, the ratio between corresponding heights is also equal to k:

 

DF = k * AH (DF corresponds to the height in EBF and AH corresponds to the height in EAD with respect to bases BE and AE, respectively)

 

Substituting and Solving for AE:

 

We can substitute the expression for DF from step 5 into the equation for the area of triangle EBF from step 4:

 

8 = BE * (k * AH)

 

8 = (k * AE) * (k * AH) (substitute BE with k * AE from step 3)

 

8 = k^2 * AE * AH

 

Since k ≠ 0 (otherwise, the triangles wouldn't be similar), we can divide both sides by k^2 * AH:

 

AE = 8 / (k^2 * AH)

 

Area of Triangle EAD:

 

We are given that the area of triangle EAD is 9. Using the same formula for the area of a triangle as before:

 

9 = (AE * AH) / 2

 

18 = AE * AH (multiply both sides by 2)

 

Substitute and Solve for AH:

 

We can substitute the expression for AE from step 6 into the equation for the area of triangle EAD from step 7:

 

18 = (8 / (k^2 * AH)) * AH

 

18 = 8 / k^2

 

k^2 = 8 / 18 = 4 / 9

 

Since we found k to be ± (2/3) in step 2, in this case, k = 2/3 (the positive value makes sense since it represents a ratio of side lengths where the corresponding side in EBF is shorter than the corresponding side in EAD).

 

Area of Parallelogram ABCD:

 

The area of a parallelogram is equal to the base times the height. Since AD is parallel to BC, the height of parallelogram ABCD is the same as the height (AH) of triangle EAD that we just solved for.

 

The base of parallelogram ABCD is the same length as side AE of triangle EAD that we also solved for. Therefore:

 

Area(ABCD) = AE * AH = 8 * 9/4 = 18.

Apr 19, 2024
 #1
avatar+1588 
0

Let the roots of Babette's monic quadratic be r and s. Since the leading coefficient is 1, the quadratic can be written as:

 

p(x)=(x−r)(x−s)=x2−(r+s)x+rs.

 

We are given that squaring the roots gives another monic quadratic with those squares as its roots. In other words:

 

(x−r2)(x−s2)=x2−(r2+s2)x+r2s2

 

Expanding the left side gives:

 

x2−(r2+2rs+s2)x+r2s2

 

Equating the coefficients of the corresponding terms in both quadratics, we get the system of equations:

 

r+s=r2+s2

 

r2s2=rs (notice this simplifies to r2s2−rs=0)

 

From the first equation, we can rearrange to get r2+s2−r−s=0. Factoring this gives (r−1)(s−1)=0. This means either r=1 or s=1.

 

We can consider two cases:

 

Case 1: r=1

 

Substituting r=1 into the second equation gives s2−s=0, which factors as s(s−1)=0. This means either s=0 or s=1. However, if s=0, then the leading coefficient of the quadratic wouldn't be 1, so we reject this case.

 

Therefore, in this case, s=1 and the quadratic is simply x2−2x+1=(x−1)2. There is only 1​ quadratic possible in this case.

 

Case 2: s=1

 

Substituting s=1 into the second equation gives r2−r=0, which factors as r(r−1)=0. This means either r=0 or r=1. However, if r=0, then the leading coefficient of the quadratic wouldn't be 1, so we reject this case.

 

Therefore, in this case, r=1 and the quadratic is again simply x2−2x+1=(x−1)2. There is only 1​ quadratic possible in this case.

 

Since both cases lead to only one possible quadratic, Babette could have been thinking of at most 2​ different monic quadratics.

Apr 19, 2024

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