Question

如果一个矩形的长和宽都增加 $10\%$ ，那么这个矩形的周长增加了

If the length and width of a rectangle are each increased by $10\%,$ then the perimeter of the rectangle is increased by

$1\%$

$10\%$

$20\%$

$21\%$

$40\%$

新周长是 $2(1.1\ell + 1.1w) = 1.1 \cdot 2(\ell + w)$ ，也就是旧周长的 $1.1$ 倍。

这表示增加了 $10\%$ 。

所以正确答案是 B。

The new perimeter is $2(1.1\ell + 1.1w) = 1.1 \cdot 2(\ell + w),$ which is $1.1$ times the old perimeter.

That is a $10\%$ increase.

Thus, the correct answer is B .