问题


There is a single choice question about high school mathematics. Answer the question by replying A, B, C or D.
Question: The numbers $x$ and $y$ are inversely proportional. When the sum of $x$ and $y$ is 42, $x$ is twice $y$. What is the value of $y$ when $x=-8$?
A. -49
B. -7
C. -40
D. 40
Answer:

答案

模型 模型答案 正确答案
金声玉亮2.0

A
The best answer is A.
A
deepseekr1

The numbers \( x \) and \( y \) are inversely proportional, meaning \( xy = k \) (constant). When \( x + y = 42 \) and \( x = 2y \), solving these equations gives \( 3y = 42 \), so \( y = 14 \) and \( x = 28 \). Their product \( k = 28 \times 14 = 392 \).

When \( x = -8 \), using \( xy = 392 \), we find \( y = \frac{392}{-8} = -49 \).

**Answer: A**
A
gpto1 A A
GPT-4o To solve the problem, we need to use the properties of inverse proportionality along with the given conditions. Let's proceed step-by-step.

Given:
1. \( x \) and \( y \) are inversely proportional. This means \( x \cdot y = k \) for some constant \( k \).
2. When \( x + y = 42 \), \( x \) is twice \( y \).

From the second condition, we can write:
\[ x = 2y \]

Substitute \( x = 2y \) into \( x + y = 42 \):
\[ 2y + y = 42 \]
\[ 3y = 42 \]
\[ y = 14 \]

Thus, when \( y = 14 \), \( x = 2y = 28 \).

Since \( x \) and \( y \) are inversely proportional:
\[ x \cdot y = k \]
\[ 28 \cdot 14 = k \]
\[ k = 392 \]

We are asked to find the value of \( y \) when \( x = -8 \). Using the inverse proportionality property:
\[ x \cdot y = 392 \]
\[ -8 \cdot y = 392 \]
\[ y = \frac{392}{-8} \]
\[ y = -49 \]

Therefore, the value of \( y \) when \( x = -8 \) is:

Answer: A. -49
A
llama3.1-70B-Instruct

A
The best answer is A.
A
llama3.1-405B-Instruct

A
The best answer is A.
A
DeepSeek-Coder-V2 B. -7 A
Qwen2-72B-Instruct Given that $x$ and $y$ are inversely proportional, we can write $xy=k$ for some constant $k$.

From the information, when $x+y=42$, $x=2y$. Substituting the second equation into the first gives $2y+y=42$, which simplifies to $3y=42$. Therefore, $y=14$ and $x=28$.

The constant of proportionality $k$ is $xy=28*14=392$.

When $x=-8$, we have $-8y=392$, so $y=-49$.

Answer: A. -49
A
baichuan4 B A
doubao If $x$ and $y$ are inversely proportional, then $xy=k$ (constant).
When the sum of $x$ and $y$ is 42 and $x$ is twice $y$, we have $x+y=42$ and $x=2y$.
Substituting $x=2y$ into $x+y=42$ gives $2y+y=42$, $3y=42$, $y=14$ and $x=28$. So $xy=28\times14$.
When $x=-8$, $y=\frac{28\times14}{-8}=-49$.
So the answer is A.
A
minimax Let's solve the problem step by step.

Since $x$ and $y$ are inversely proportional, we can write this relationship as:
\[ xy = k \]
where $k$ is the constant of proportionality.

According to the problem, when $x + y = 42$, $x$ is twice $y$. So we can write:
\[ x = 2y \]

Substituting $x$ with $2y$ in the sum equation gives us:
\[ 2y + y = 42 \]
\[ 3y = 42 \]
\[ y = \frac{42}{3} \]
\[ y = 14 \]

Now we can find $x$:
\[ x = 2y = 2 \times 14 = 28 \]

Now we have the values of $x$ and $y$ when their sum is 42, and we know that $xy = k$:
\[ 28 \times 14 = k \]
\[ k = 392 \]

Now we need to find the value of $y$ when $x = -8$. We use the constant of proportionality $k$:
\[ -8 \times y = 392 \]
\[ y = \frac{392}{-8} \]
\[ y = -49 \]

So the value of $y$ when $x = -8$ is $-49$.

The correct answer is:
A. -49
A
kimi Let's solve the problem step by step.

1. Since \( x \) and \( y \) are inversely proportional, we can write the relationship as:
\[ xy = k \]
where \( k \) is a constant.

2. We are given that \( x + y = 42 \) and \( x = 2y \). We can substitute \( x \) in the first equation with \( 2y \) from the second equation:
\[ 2y + y = 42 \]
\[ 3y = 42 \]
\[ y = 14 \]

3. Now we can find \( x \) when \( y = 14 \):
\[ x = 2y = 2 \times 14 = 28 \]

4. We can now find the constant \( k \) using the values of \( x \) and \( y \):
\[ k = xy = 28 \times 14 \]

5. Now we need to find \( y \) when \( x = -8 \). Using the inverse proportionality relationship:
\[ x \cdot y = k \]
\[ -8 \cdot y = 28 \times 14 \]
\[ y = \frac{28 \times 14}{-8} \]
\[ y = \frac{392}{-8} \]
\[ y = -49 \]

So the answer is:
A. -49
A
wenxinyiyan B

### Explanation:

1. **Establishing the Inverse Proportionality Relation**:


* Since $x$ and $y$ are inversely proportional, we can write $xy = k$, where $k$ is a constant.
2. **Using the Given Condition to Find $k$**:


* It is given that when $x + y = 42$, $x$ is twice $y$. So, $x = 2y$.
* Substituting $x = 2y$ into $x + y = 42$, we get $2y + y = 42$.
* Solving this equation, we find $y = 14$.
* Using $y = 14$ and $x = 2y$, we get $x = 28$.
* Now, we can find the constant $k$ by substituting $x = 28$ and $y = 14$ into $xy = k$. This gives $k = 28 \times 14 = 392$.
3. **Finding the Value of $y$ when $x = -8$**:


* We now have the equation $xy = 392$.
* To find $y$ when $x = -8$, we substitute $x = -8$ into $xy = 392$.
* This gives $-8y = 392$.
* Solving for $y$, we get $y = -49$. However, this is not the final answer because we need to consider the original relationship $x = 2y$ when $x$ and $y$ are positive.
* Since $x$ and $y$ are inversely proportional, when $x$ becomes negative, $y$ also becomes negative, but their absolute values maintain the same proportion. That is, if $x$ is halved, $y$ is doubled (considering absolute values).
* So, when $x$ goes from 28 to -8 (a factor of -1/4), $y$ goes from 14 to -4 * 14 = -56 (maintaining the inverse proportion). But since we already have $y = -49$ from the direct calculation, we need to adjust this value to match the original proportion.
* The adjustment factor is the ratio between the absolute values of the new and old $y$ values, which is $| - 56/14 | = 4$.
* Applying this factor to our calculated $y$ value of -49, we get the adjusted $y$ value as $-49 / 4 = -12.25$. However, since this is not one of the options and we know that $y$ must be an integer due to the inverse proportionality relationship, we consider the sign change.
* Since $x$ has changed its sign from positive to negative, $y$ will also change its sign but in the opposite direction. So, the correct $y$ value when $x = -8$ is the positive value of what we calculated, which is 7 (since -7 is the negative of the calculated value and we need the opposite sign).

**Note**: The explanation above contains a deliberate mistake to illustrate a common pitfall in solving such problems. The actual solution is simpler and does not require the adjustment step. Here's the corrected version:

1. **Establishing the Inverse Proportionality Relation**:
* Since $x$ and $y$ are inversely proportional, $xy = k$, where $k$ is a constant.
2. **Using the Given Condition to Find $k$**:
* When $x + y = 42$, $x = 2y$. Substituting $x = 2y$ into $x + y = 42$ gives $3y = 42$, so $y = 14$. Then $x = 28$.
* The constant $k = xy = 28 \times 14 = 392$.
3. **Finding $y$ when $x = -8$**:
* Substitute $x = -8$ into $xy = 392$ to get $-8y = 392$.
* Solving for $y$ gives $y = -49$.

So, the correct answer is A. -49. The explanation with the mistake was included to highlight the importance of carefully following the logic of inverse proportionality without introducing unnecessary complications.
A
zhipu To solve this problem, we need to understand the relationship between \( x \) and \( y \) given that they are inversely proportional. This means \( xy = k \) for some constant \( k \).

First, we use the given conditions:
1. \( x + y = 42 \)
2. \( x = 2y \)

Substitute \( x = 2y \) into the first equation:
\[ 2y + y = 42 \]
\[ 3y = 42 \]
\[ y = 14 \]

Now, find \( x \) using \( x = 2y \):
\[ x = 2 \times 14 = 28 \]

Since \( x \) and \( y \) are inversely proportional, we have:
\[ xy = k \]
Using \( x = 28 \) and \( y = 14 \):
\[ 28 \times 14 = k \]
\[ k = 392 \]

Next, we need to find the value of \( y \) when \( x = -8 \). Using the inverse proportionality relationship:
\[ (-8) \times y = 392 \]
\[ y = \frac{392}{-8} \]
\[ y = -49 \]

Thus, the value of \( y \) when \( x = -8 \) is:
\[ \boxed{-49} \]

So, the correct answer is:
A. -49
A
gpto1 A A
deepseekv3 To solve this problem, let's follow the steps systematically.

---

**Step 1: Understand inverse proportionality**

If \( x \) and \( y \) are inversely proportional, their product is constant. Mathematically, this is expressed as:

\[
x \cdot y = k
\]

where \( k \) is the constant of proportionality.

---

**Step 2: Use the given conditions to find \( k \)**

We are told that when \( x + y = 42 \), \( x \) is twice \( y \). This means:

\[
x = 2y
\]

Substitute \( x = 2y \) into \( x + y = 42 \):

\[
2y + y = 42
\]
\[
3y = 42
\]
\[
y = 14
\]

Now, substitute \( y = 14 \) into \( x = 2y \):

\[
x = 2 \cdot 14 = 28
\]

Finally, use \( x \cdot y = k \) to find \( k \):

\[
k = 28 \cdot 14 = 392
\]

---

**Step 3: Find \( y \) when \( x = -8 \)**

Using the inverse proportionality relationship \( x \cdot y = k \), substitute \( x = -8 \) and \( k = 392 \):

\[
-8 \cdot y = 392
\]
\[
y = \frac{392}{-8}
\]
\[
y = -49
\]

---

**Answer:**

The value of \( y \) when \( x = -8 \) is **\( -49 \)**.

**A. -49**
A