Question

当 $x=7$ 时，下列哪一个最小？

For $x=7,$ which of the following is the smallest?

$\dfrac{6}{x}$

$\dfrac{6}{x+1}$

$\dfrac{6}{x-1}$

$\dfrac{x}{6}$

$\dfrac{x+1}{6}$

代入题给的值，逐项比较。

A: $\dfrac 6x = \dfrac 67$ 。

B: $\dfrac 6{x+1} = \dfrac 68$ 。

C: $\dfrac 6{x-1} = 1$ 。

D: $\dfrac x6 = \dfrac 76$ 。

E: $\dfrac {x+1}6 = \dfrac{4}{3}$ 。

其中最小的是六除以八，也就是四分之三，所以正确答案是 B。

If we plug in the values into each answer choice, we get the following:

A: $\dfrac 6x = \dfrac 67$

B: $\dfrac 6{x+1} = \dfrac 68$

C: $\dfrac 6{x-1} = 1$

D: $\dfrac x6 = \dfrac 76$

E: $\dfrac {x+1}6 = \dfrac{4}{3}$

Thus, the correct answer is B .