Question

如果玫瑰丛之间大约相隔 $1$ 英尺，那么要围住一个半径为 $12$ 英尺的圆形露台，大约需要多少丛玫瑰？

If rose bushes are spaced about $1$ foot apart, approximately how many bushes are needed to surround a circular patio whose radius is $12$ feet?

$12$

$38$

$48$

$75$

$450$

玫瑰丛围绕圆形边缘，所以数量约等于周长 $2\pi r = 2\pi(12)$ 。

取 $\pi \approx 3.14$ ，约为 $2 \times 3.14 \times 12 \approx 75$ 英尺，所以大约需要 $75$ 丛。

所以正确答案是 D。

The bushes surround the circular edge, so their number is about the circumference $2\pi r = 2\pi(12).$

Using $\pi \approx 3.14,$ this is about $2 \times 3.14 \times 12 \approx 75$ feet, so roughly $75$ bushes are needed.

Thus, the correct answer is D .