跟读练习: Math Antics - What Are Percentages? - 通过视频学习英语口语
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Hi! Welcome to Math Antics.
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Now that you know all about fractions, from watching all of our fractions videos, it’s time to learn about something called “percentages”.
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Percentages are super important.
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Have you ever been in a math class and heard another student ask the teacher: Um.. excuse me… teacher… Ah… when are we ever gonna use this stuff?
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Ya know… like in real life?
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Well when it comes to percentages, the answer is one-hundred percent of the time.
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Well alright… maybe not a hundred percent of the time… but a lot!
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Percentages are used every day to calculate things like: …how much sales tax you pay when you buy something.
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…how much something costs when it’s on sale.
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…how much fiber is in your granola bar.
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…or how much money you can make if you invest it in the stock market.
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That’s all real life stuff for sure.
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So, you can see that it’s really important to understand percentages and how we use them in math.
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Alright then… are you ready to learn the key to understanding percentages, or percents as they’re called for short?
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Drum roll please… A percent is a fraction!
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Whaaaat? That’s right… a percent IS a fraction!
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And since you already know all about fractions, learning about percents is gonna be easy.
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But a percent isn’t just any old fraction. A percent is a special fraction that always has 100 as the bottom number.
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If it’s a percent, then no matter what the top number is, the bottom number will be 100.
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In fact, because the bottom number of a percent is always 100, we don’t even write it.
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Instead, we use this handy little symbol (%) called a percent sign.
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Whenever you see this symbol after a number, it means the number is a percent.
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It’s really a fraction with 100 on the bottom, but it’s just being written in this more compact form.
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...like this number 15 here.
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It’s got the percent sign after it, so we read it as "15 percent", and because a percent is really a fraction that always has 100 as the bottom number, we know that it means the same thing as 15 over 100.
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Percents make even more sense if you know what the word precent means.
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The prefix of the word (per) means “for each” or “for every”. Ya know like if someone said, “only one cookie per person”.
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And the root word (cent) is Latin for 100. That’s why there’s 100 cents in a dollar.
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So, percent literally means “per 100” and that’s why they’re shortcuts for writing fractions that have 100 as the bottom number.
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Alright then, so whenever you see a percent like this, you know it can be replaced with (or converted) to a fraction.
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Let’s look at a few examples so you see the pattern.
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3% means 3 over 100 10% means 10 over 100 25% means 25 over 100 and 75% means 75 over 100 These are percents… and these are the fractions that they stand for.
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There’s a few other interesting percents that we should take a look at.
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…like this one: 0% …can you have 0% ?
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Yes! 0% would just mean 0 over 100. It’s what we like to call a “zero fraction” cuz its value is just zero.
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Remember, it’s okay to have zero on the top of a fraction, but not the bottom!
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Alright then, what about 100%. Well 100% just means 100 over 100. That’s what we like to call a “whole fraction”.
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The top number is the same as the bottom, so its value is just one whole, or 1.
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Okay then, 0% is just zero, and 100% is just 1.
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But what about numbers bigger than 100? Can you have 126% ?
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Yep, it works exactly the same way. 126% just means 126 over 100.
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And you know from the fractions videos, that’s what we call an “improper fraction”.
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The top number is bigger than the bottom number, so the fraction’s value will be greater than 1.
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Alright team, I want you to go out there and give me a-hundred and TEN percent effort in today's game!
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But coach… it would be “improper” for us to give a-hundred and ten percent effort in today’s game.
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Okay, so now you know the key to percentages. …that they’re just special fractions that always have 100 as the bottom number.
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But there’s one more thing that I need to tell you about in this video, and that’s decimals.
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Do you remember in the video about fractions and decimals that you can convert any fraction into its decimal value?
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Sometimes it was kind of tricky converting to a decimal if we had to divide the top number by the bottom number.
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But other times, like when we had “base-10” fractions, it was easy because decimal number places are made for counting base-10 fractions, (like tenths, hundredths and thousandths).
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Well guess what… Percents ARE base-10 fractions! They are hundredths because their bottom number is always 100.
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That means it’s really easy to re-write a percentage as a decimal number.
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You can do it the same way as we did in the base-10 fractions video.
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For example, we know that 15% is just 15 over 100, right? That’s its fraction form.
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But it also has the decimal form 0.15 because THIS is the hundredths place and 0.15 means 15 hundredths.
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So, we can re-write 15% as a fraction (15 over 100) OR as a decimal (0.15) And now that you know WHY we can easily convert a percentage to a decimal, let me show you a really simple trick for doing it.
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First, you start with the number in percent form like this: 35% Next, you imagine where the decimal point should be in the number 35.
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It’s not shown, but if it was, it would be right here next to the ones place.
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(Now remember, 35 and 35.0 are the same value.) Now that you know where the decimal point is, just move it two number places to the left (away from the percent symbol) and draw it in right there.
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Last of all, once you have moved the decimal point, you erase the percent sign because you don’t have a percent anymore.
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Moving the decimal point two places to the left converted it into the decimal value of that percent.
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Let’s try converting a few more percents into their decimal values so you can get the hang of it.
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For 62 percent, we move the decimal point two places to the left and get 0.62 (Remember, we can put an extra zero in front of the decimal point to be a place holder and to make the decimal point easier to notice.) For 75 percent, we move the decimal point and get 0.75 For 99 percent, we move the decimal point to get 0.99 Pretty Cool, huh?
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Okay, but what about 4% ? You might wonder how we can move the decimal point two places over when our number only has one digit.
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But all we need to do is use a zero as a place holder in the number place that’s missing.
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Then, when we move the decimal point two places over, we end up with the decimal value of 0.04.
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Now that makes sense because 4 is in the hundredths place and 4% is 4 over 100.
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And in the same way, 1% would just be 0.01. Again, we need that extra zero placeholder.
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Here’s a few more interesting examples: 0% would be just 0.00 And if we have 100% and we move the decimal point two places to the left, we end up with 1.00 But 1.00 is the same value as 1. That’s why 100% represent one whole.
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And if we have 142%, we move the decimal point to get 1.42 That’s a value greater than one which is what we’d expect because 142% is really an improper fraction (142 over 100) Its value should be greater than 1.
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Alright, so now you know that a percent is a special fraction that always has 100 as the bottom number.
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And you know that you can re-write percents in either their fraction form OR their decimal form.
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25% is 25 over 100 or 0.25 But keep in mind that you could go the other way too.
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If someone gives you a fraction with 100 as the bottom number, you can re-write it in percent form.
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If you get 12 over 100, you can say that’s 12% And if you get 80 over 100, you can say that’s 80% OR… If you get the decimal 0.10, you can say that’s 10% and if you get the decimal 0.38, you can say that’s 38% So, that’s the key to percentages. They’re another way to write fractions and decimals.
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But there’s a lot more to learn about how they‘re used in math, and we’ll learn more about that in the next few videos.
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But for now, you should be sure that you really understand the basics of percentages by doing the exercises for this section.
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Thanks for watching Math Antics, and I’ll see ya next time!
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Learn more at www.mathantics.com
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关于本节课
在本节课中，您将学习关于百分比的重要知识。百分比与分数之间的关系将帮助您更轻松地理解数学中的各种概念。您将了解到百分比是如何在日常生活中使用的，比如购买商品的销售税，了解食品中的营养成分，或者投资于股市能获得多少收益。通过了解和练习，您能够在生活中自信地应用这些知识，同时提升您的英语口语能力。
关键词汇与短语
- 百分比 (percent): 表示每一百中有多少的量。
- 分数 (fraction): 一种数学表达方式，表示部分与整体的关系。
- 销售税 (sales tax): 购买商品时需要支付的额外费用。
- 投资 (investment): 将资金投入某个项目或市场以获得收益的行为。
- 零分数 (zero fraction): 分子为零的分数。
- 完整分数 (whole fraction): 分子与分母相等的分数。
- 不规则分数 (improper fraction): 分子大于分母的分数。
- 每个 (per): 表示分配或比例的用法，与“百分比”紧密相关。
练习建议
在进行口语练习时，您可以使用 shadow speak 的方法来增强您的发音和流利度。首先，观看这段关于百分比的 看YouTube学英语 视频，并尝试在每次观看时跟着说。视频中的语速适中，发音清晰，非常适合进行 shadowing 练习。尽量模仿视频中讲者的语调和情感，使练习更具真实感。
同时，在练习时，可以使用 shadowspeak 技巧，即在重复句子时尝试添加自己的例子，例如自己购物时所付的税率或投资的想法。这种结合真实生活的练习能帮助您更牢固地掌握内容，提升对英语的理解和应用能力。通过不断反复，您会发现在表达与碰到百分比相关的问题时，将变得更加自信与自然。
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | being written · can be replaced · are made |
| 用 “should” 提建议 should + 动词 — 表示应该做的事 | should take · should be |
| 比较级 -er than / more … than — 比较两个事物 | bigger than · greater than |
| “will” 表将来 will + 动词 — 决定、承诺或预测 | will be · we'll learn · I'll see |
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。