Probability
概率
Probability measures how likely something is to happen. In this lesson you will learn how to calculate probability and describe it with words like certain and impossible.
概率量度事情發生的可能性。在這一課，你會學習怎樣計算概率，並用「必然」和「不可能」等詞語來描述。
1 · What is probability?
甚麼是概率？
Probability is always between 0 and 1. A probability of 0 means impossible, and 1 means certain. We can also write it as a fraction, decimal or percentage.
概率總是在 0 和 1 之間。概率 0 代表不可能，1 代表必然。我們也可以用分數、小數或百分數來表示。
2 · Calculating probability
計算概率
Probability = favourable outcomes ÷ total outcomes. When you roll a die, the probability of rolling a 3 is 1 out of 6.
概率 = 有利結果的數目 ÷ 結果總數。擲一粒骰子時，擲出 3 的概率是六分之一。
A die has 6 faces, so P(rolling a 3) = 1/6.
骰子有 6 面，所以 P（擲出 3）= 1/6。
3 · From certain to impossible
由必然到不可能
We describe probability with words:
我們用詞語來描述概率：
- Certain — it will definitely happen.必然——一定發生。
- Likely — it will probably happen.很可能——大概會發生。
- Unlikely — it probably will not happen.不太可能——大概不會發生。
- Impossible — it cannot happen.不可能——不會發生。
4 · Coins and dice
硬幣與骰子
A fair coin has 2 outcomes, so the probability of heads is 1/2. A die has 6 outcomes, so the probability of rolling any one number is 1/6.
一枚公平的硬幣有 2 個結果，所以擲出正面的概率是 1/2。一粒骰子有 6 個結果，所以擲出任何一個數字的概率是 1/6。
5 · Quick check
小測驗