问题


There is a single choice question about high school mathematics. Answer the question by replying A, B, C or D.
Question: Positive integers $x$ and $y$ have a product of 56 and $x < y$. Seven times the reciprocal of the smaller integer plus 14 times the reciprocal of the larger integer equals 4. What is the value of $x$?
A. 13
B. 14
C. 1
D. 2
Answer:

答案

模型 模型答案 正确答案
金声玉亮2.0

We have $xy=56$ and $\frac{7}{x}+\frac{14}{y}=4$. Multiplying both sides of the second equation by $xy$ gives $7y+14x=4xy$. Substituting $xy=56$ into this equation gives $7y+14x=4\cdot56=224$. Since $x$ and $y$ are positive integers, we can guess and check to find the solution. If $x=1$, then $7y+14=224$, so $7y=210$, so $y=30$. But then $xy=1\cdot30=30\neq56$, so $x\neq1$. If $x=2$, then $7y+28=224$, so $7y=196$, so $y=28$. But then $xy=2\cdot28=56$, so $x=2$ is a solution. Since $x<y$, we have $x=\boxed{2}$.
The best answer is D.
D
deepseekr1

The problem involves finding positive integers \( x \) and \( y \) such that \( xy = 56 \), \( x < y \), and \( \frac{7}{x} + \frac{14}{y} = 4 \). Listing factor pairs of 56 with \( x < y \): \((1, 56)\), \((2, 28)\), \((4, 14)\), \((7, 8)\). Testing each pair:

1. For \( x = 1 \), \( y = 56 \):
\( \frac{7}{1} + \frac{14}{56} = 7 + 0.25 = 7.25 \neq 4 \).

2. For \( x = 2 \), \( y = 28 \):
\( \frac{7}{2} + \frac{14}{28} = 3.5 + 0.5 = 4 \), which satisfies the equation.

3. For \( x = 4 \), \( y = 14 \):
\( \frac{7}{4} + \frac{14}{14} = 1.75 + 1 = 2.75 \neq 4 \).

4. For \( x = 7 \), \( y = 8 \):
\( \frac{7}{7} + \frac{14}{8} = 1 + 1.75 = 2.75 \neq 4 \).

Only \((2, 28)\) works. Thus, \( x = 2 \).

**Answer:** D
D
gpto1 D D
GPT-4o To solve this problem, we need to use the given conditions to find the values of \( x \) and \( y \).

1. The product of \( x \) and \( y \) is 56:
\[
xy = 56
\]

2. \( x \) is the smaller integer and \( y \) is the larger integer:
\[
x < y
\]

3. Seven times the reciprocal of \( x \) plus fourteen times the reciprocal of \( y \) equals 4:
\[
\frac{7}{x} + \frac{14}{y} = 4
\]

First, let's express \( y \) in terms of \( x \) using the product equation:
\[
y = \frac{56}{x}
\]

Substitute \( y = \frac{56}{x} \) into the reciprocal equation:
\[
\frac{7}{x} + \frac{14}{\frac{56}{x}} = 4
\]

Simplify the second term:
\[
\frac{7}{x} + \frac{14x}{56} = 4
\]

Since \( \frac{14}{56} \) simplifies to \( \frac{1}{4} \), the equation becomes:
\[
\frac{7}{x} + \frac{x}{4} = 4
\]

To clear the fractions, multiply every term by 4:
\[
4 \cdot \frac{7}{x} + 4 \cdot \frac{x}{4} = 4 \cdot 4
\]

This simplifies to:
\[
\frac{28}{x} + x = 16
\]

Multiply every term by \( x \) to clear the fraction:
\[
28 + x^2 = 16x
\]

Rearrange to form a quadratic equation:
\[
x^2 - 16x + 28 = 0
\]

Solve the quadratic equation using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a = 1 \), \( b = -16 \), and \( c = 28 \):
\[
x = \frac{16 \pm \sqrt{(-16)^2 - 4 \cdot 1 \cdot 28}}{2 \cdot 1}
\]
\[
x = \frac{16 \pm \sqrt{256 - 112}}{2}
\]
\[
x = \frac{16 \pm \sqrt{144}}{2}
\]
\[
x = \frac{16 \pm 12}{2}
\]

This gives us two potential solutions:
\[
x = \frac{16 + 12}{2} = 14
\]
\[
x = \frac{16 - 12}{2} = 2
\]

Since \( x \) must be the smaller integer, we select \( x = 2 \).

Therefore, the value of \( x \) is:
\[
\boxed{2}
\]

So, the answer is:
D. 2
D
llama3.1-70B-Instruct

Answer: D
D
llama3.1-405B-Instruct

We have $xy=56$ and $\frac{7}{x}+\frac{14}{y}=4$. Multiplying both sides of the second equation by $xy$ gives $7y+14x=4xy$. Substituting $xy=56$ into this equation gives $7y+14x=4\cdot56=224$. Since $x$ and $y$ are positive integers, we can guess and check to find the solution. If $x=1$, then $y=56$, but $7\cdot56+14\cdot1=406\neq224$. If $x=2$, then $y=28$, and $7\cdot28+14\cdot2=224$. Therefore, the answer is $\boxed{\textbf{(D) }2}$.
The best answer is D.
D
DeepSeek-Coder-V2 D. 2 D
Qwen2-72B-Instruct D. 2

The pairs of positive integers whose product is 56 are (1, 56), (2, 28), (4, 14), (7, 8). Given $x < y$, the only pairs to consider are (1, 56), (2, 28), (4, 14), and (7, 8). We need to find a pair that satisfies the equation $7\left(\frac{1}{x}\right) + 14\left(\frac{1}{y}\right) = 4$. Plugging the pairs into the equation, we find that only the pair (2, 28) satisfies the equation. Therefore, $x = 2$.
D
baichuan4 Let's denote the reciprocals of $x$ and $y$ as $\frac{1}{x}$ and $\frac{1}{y}$ respectively.

Since $x$ and $xy$ have a product of 56, we have:
$$xy = 56$$

And the equation given in the problem is:
$$7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4$$

We can rewrite this equation as:
$$\frac{7}{x} + \frac{14}{y} = 4$$

Now, since $x < y$, the reciprocal of $x$ is larger than the reciprocal of $y$, so we can assume that $\frac{7}{x}$ is the larger term in the sum. Therefore, to make the sum approximately 4, $\frac{7}{x}$ should be approximately 3.5, which means $x$ should be approximately 2.

So, the answer is D. 2.
D
doubao Let's assume $x$ is the smaller integer and $y$ is the larger integer. The product of $x$ and $y$ is 56, so $xy=56$. The equation given is $\frac{7}{x}+\frac{14}{y}=4$. We can substitute $y=\frac{56}{x}$ into the equation: $\frac{7}{x}+\frac{14}{\frac{56}{x}}=4$. Solving this equation gives $x=1$ or $x=14$. Since $x<y$ and $xy=56$, $x=1$ and $y=56$. So the answer is C. D
minimax Let's denote the smaller integer as $x$ and the larger integer as $y$. We are given that $x \cdot y = 56$ and $x < y$. We are also given that $7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4$.

First, let's solve the equation $7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4$ for $x$ and $y$.

Multiplying through by $xy$ to clear the denominators, we get:

$7y + 14x = 4xy$

Since $x \cdot y = 56$, we can substitute $56$ for $xy$:

$7y + 14x = 4 \cdot 56$

$7y + 14x = 224$

Now, let's divide the entire equation by 7 to simplify:

$y + 2x = 32$

We know that $x$ and $y$ are positive integers, and $x < y$. Let's find pairs of integers $(x, y)$ that multiply to 56 and satisfy $x < y$.

The pairs are (1, 56), (2, 28), (4, 14), and (7, 8). We can eliminate (1, 56) because it does not satisfy $x < y$. Now let's check the remaining pairs in the equation $y + 2x = 32$:

For (2, 28): $28 + 2(2) = 28 + 4 = 32$ (satisfies the equation)
For (4, 14): $14 + 2(4) = 14 + 8 = 22$ (does not satisfy the equation)
For (7, 8): $8 + 2(7) = 8 + 14 = 22$ (does not satisfy the equation)

The only pair that satisfies both the product condition and the equation is (2, 28). Therefore, the value of $x$ is 2.

Answer: D. 2
D
kimi Let's solve the problem step by step.

Given:
1. \( x \cdot y = 56 \)
2. \( x < y \)
3. \( 7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4 \)

From the third equation, we can rewrite it as:
\[ \frac{7}{x} + \frac{14}{y} = 4 \]

Multiplying through by \( xy \) to clear the denominators, we get:
\[ 7y + 14x = 4xy \]

Now, we know from the first equation that \( xy = 56 \), so we can substitute that in:
\[ 7y + 14x = 4 \cdot 56 \]
\[ 7y + 14x = 224 \]

We also know that \( x \cdot y = 56 \), so we can list the pairs of factors of 56 that satisfy \( x < y \):
\( (1, 56), (2, 28), (4, 14), (7, 8) \)

Since \( x < y \), we can eliminate the pairs where \( x \) is greater than \( y \), leaving us with:
\( (1, 56), (2, 28), (4, 14), (7, 8) \)

Now we can test these pairs in the equation \( 7y + 14x = 224 \):

For \( (1, 56) \):
\[ 7 \cdot 56 + 14 \cdot 1 = 392 + 14 = 406 \] (Not equal to 224)

For \( (2, 28) \):
\[ 7 \cdot 28 + 14 \cdot 2 = 196 + 28 = 224 \] (This is equal to 224)

For \( (4, 14) \):
\[ 7 \cdot 14 + 14 \cdot 4 = 98 + 56 = 154 \] (Not equal to 224)

For \( (7, 8) \):
\[ 7 \cdot 8 + 14 \cdot 7 = 56 + 98 = 154 \] (Not equal to 224)

The only pair that satisfies all the conditions is \( (2, 28) \), so \( x = 2 \).

Answer: D. 2
D
wenxinyiyan D. 2
Let $x$ and $y$ be the two positive integers such that $xy = 56$ and $x < y$.
According to the question, we have the equation:
$\frac{7}{x} + \frac{14}{y} = 4$Multiply both sides by $xy$ to eliminate the fractions:
$7y + 14x = 4xy$Since $xy = 56$, we can substitute this value into the equation:
$7y + 14x = 4 \times 56$$7y + 14x = 224$Divide both sides by 7 to simplify:
$y + 2x = 32$Now, we need to solve this equation together with $xy = 56$ and $x < y$.
Let's consider the factors of 56: $1 \times 56$, $2 \times 28$, $4 \times 14$, $7 \times 8$.
Since $x < y$, we can quickly identify that $x = 2$ and $y = 28$ satisfy all the conditions:
$xy = 2 \times 28 = 56$
$y + 2x = 28 + 2 \times 2 = 32$
$x < y$ (i.e., $2 < 28$)
Therefore, the value of $x$ is 2.
D
zhipu To solve the problem, we need to find the positive integers \( x \) and \( y \) such that:

1. \( x \cdot y = 56 \)
2. \( x < y \)
3. \( 7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4 \)

First, let's rewrite the equation from condition 3 in a more convenient form:
\[ 7 \cdot \frac{1}{x} + 14 \cdot \frac{1}{y} = 4 \]
Dividing through by 7, we get:
\[ \frac{1}{x} + 2 \cdot \frac{1}{y} = \frac{4}{7} \]

Now, substitute \( y = \frac{56}{x} \) (from \( x \cdot y = 56 \)) into the equation:
\[ \frac{1}{x} + 2 \cdot \frac{1}{\frac{56}{x}} = \frac{4}{7} \]
Simplify the second term:
\[ \frac{1}{x} + 2 \cdot \frac{x}{56} = \frac{4}{7} \]
\[ \frac{1}{x} + \frac{x}{28} = \frac{4}{7} \]

To clear the fractions, multiply every term by \( 28x \):
\[ 28 + x^2 = 16x \]
Rearrange to form a quadratic equation:
\[ x^2 - 16x + 28 = 0 \]

Now, solve the quadratic equation using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a = 1 \), \( b = -16 \), and \( c = 28 \):
\[ x = \frac{16 \pm \sqrt{(-16)^2 - 4 \cdot 1 \cdot 28}}{2 \cdot 1} \]
\[ x = \frac{16 \pm \sqrt{256 - 112}}{2} \]
\[ x = \frac{16 \pm \sqrt{144}}{2} \]
\[ x = \frac{16 \pm 12}{2} \]

This gives us two solutions:
\[ x = \frac{16 + 12}{2} = 14 \]
\[ x = \frac{16 - 12}{2} = 2 \]

Since \( x < y \), we need to check which of these values for \( x \) satisfies the condition \( x < y \):

1. If \( x = 14 \), then \( y = \frac{56}{14} = 4 \). Here, \( x \not< y \).
2. If \( x = 2 \), then \( y = \frac{56}{2} = 28 \). Here, \( x < y \).

Thus, the value of \( x \) that satisfies all conditions is \( 2 \).

So, the answer is:
\[ \boxed{2} \]
D
gpto1 D D
deepseekv3 To solve the problem, let's follow these steps:

1. **Given Information:**
- \( x \times y = 56 \)
- \( x < y \)
- \( 7 \times \frac{1}{x} + 14 \times \frac{1}{y} = 4 \)

2. **Express \( y \) in terms of \( x \):**
\[
y = \frac{56}{x}
\]

3. **Substitute \( y \) into the equation:**
\[
7 \times \frac{1}{x} + 14 \times \frac{1}{\frac{56}{x}} = 4
\]
Simplify the second term:
\[
14 \times \frac{x}{56} = \frac{14x}{56} = \frac{x}{4}
\]
So the equation becomes:
\[
\frac{7}{x} + \frac{x}{4} = 4
\]

4. **Multiply through by \( 4x \) to eliminate denominators:**
\[
28 + x^2 = 16x
\]
Rearrange to form a quadratic equation:
\[
x^2 - 16x + 28 = 0
\]

5. **Solve the quadratic equation:**
\[
x = \frac{16 \pm \sqrt{256 - 112}}{2} = \frac{16 \pm \sqrt{144}}{2} = \frac{16 \pm 12}{2}
\]
This gives two possible solutions:
\[
x = \frac{28}{2} = 14 \quad \text{or} \quad x = \frac{4}{2} = 2
\]

6. **Check the condition \( x < y \):**
- If \( x = 14 \), then \( y = \frac{56}{14} = 4 \). But \( 14 < 4 \) is false.
- If \( x = 2 \), then \( y = \frac{56}{2} = 28 \). Here, \( 2 < 28 \) is true.

7. **Conclusion:**
The valid value of \( x \) is **2**.

\boxed{D}
D