AMC10 2005 B

AMC10 2005 B · Q2

AMC10 2005 B · Q2. It mainly tests Quadratic equations, Percent.

A positive number $x$ has the property that $x\%$ of $x$ is 4. What is $x$?

一个正数$x$具有这样的性质：$x$的$x\%$是4。$x$是多少？

(A) 2 2

(B) 4 4

(D) 20 20

(E) 40 40

Answer

Correct choice: (D)

正确答案：（D）

Solution

$\frac{x}{100} \cdot x = 4$, so $x^2 = 400$. Because $x > 0$, it follows that $x = 20$.

$\frac{x}{100} \cdot x = 4$，所以$x^2 = 400$。因为$x > 0$，所以$x = 20$。

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