Re: [轉錄][新聞] 30÷2(2+3)÷5是多少? 計算機딠…
我本來也是算 0.6
但正確答案說是15
於是我開始思考自己錯在哪裡
國小學基本數學運算時,老師有教兩個數學運算的優先順序:
1. 先乘除後加減
2. 有括號先做
但可能我們都忘了附帶條件:
1.&2. 的情況同時有時,2的優先性高於1,也就是說2.是最高最廣最大的通用定則
1. 定則成立於 3x2 + 1x7 這種情況下,也就是說1.是區域定則,非通用定則
接下來回到原問題 30÷2(2+3)÷5
根據優先性最高的通用定則 題目變成 30÷2x5 ÷5
問題來了,並沒有 x + - 或 ÷+ - 這種情況,
所以 乘跟除的優先性是一樣的,化簡後的式子並無理由額外規定 乘還要先做
既然沒有了優先性的問題,根據我們算數學的習慣
從左算到右
30 除 2 = 15
15 乘 5 = 75
75 除 5 = 15
是以,最後答案為 15
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