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  3. A certain spiral staircase is designed so that each step after the first one is

A certain spiral staircase is designed so that each step after the first one is

游客2024-01-12  66
问题 A certain spiral staircase is designed so that each step after the first one is turned 20° counterclockwise from the one immediately below it, how many of the steps make up 2.5 complete revolutions?
选项 A、18
B、36
C、38
D、45
E、50
答案 D
解析 某一螺旋梯按照高一级台阶相对于低一级台阶逆时针旋转20°来设计，问2.5圈的旋梯共有多少级台阶组成?
解：本题的正确答案为(D)。“revolution”意为旋转一周，由题意可得台阶数为：360°× 2.5 ÷ 20°=45
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