Question

如果一个长方形的长增加 $20\%$ ，宽增加 $50\%$ ，那么面积增加了

If the length of a rectangle is increased by $20\%$ and its width is increased by $50\%,$ then the area is increased by

$10\%$

$30\%$

$70\%$

$80\%$

$100\%$

知识点：百分数

新长是原长的 $1.2$ 倍，新宽是原宽的 $1.5$ 倍，所以新面积是原面积的 $1.2 \times 1.5 = 1.8$ 倍。

这表示面积增加了 $80\%$ 。

所以正确答案是 D。

The new length is $1.2$ times the old and the new width is $1.5$ times the old, so the new area is $1.2 \times 1.5 = 1.8$ times the old area.

That is an increase of $80\%.$

Thus, the correct answer is D .