Pratique du Shadowing: Math Antics - Finding A Percent Of A Number - Apprendre l'anglais à l'oral avec la vidéo
Création de la leçon...
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Hi and welcome to Math Antics.
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In today’s video, we’re gonna learn how to do one of the most common calculations with percentages.
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We’re gonna learn how to find a percent of a number.
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But what does that even mean?
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Do numbers have percents that they hide somewhere and then we have to go looking for them like a game of hide and seek?
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Gottch ya! Umm - not exactly.
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Finding a percent of a number makes more sense if you remember that a number just represents an amount and that a percent is really just a fraction.
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So finding a percent of a number really means finding a fraction of an amount.
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Think about it this way… Let’s say the number 20 represents an amount, like the amount of lady bugs that you found at the park one day.
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And let’s also imagine that you agreed to give 25% of all the lady bugs you found to your little sister.
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Okay then, so how many is that?
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If you have 20 lady bugs, how many is 25% of that amount?
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That’s what it means to find a percent of a number.
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You’re finding out how much that percent (or fraction) of the total is.
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In this case, since our total is 20, we need to know what 25% of 20 is.
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So how do we figure that out?
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Well, it’s really easy if you remember back to one of our fractions videos; the one about multiplying fractions.
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In that video, we learned that when dealing with fractions, sometimes the word “of” is used instead of the multiplication symbol.
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When they say find 1/2 of 16, they really mean find 1/2 times 16.
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Well guess what… Since a percent is just a special fraction… “of” means the exact same thing with percents that it did with fractions.
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When we have 25% of 20, that means the same as 25% times 20.
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Great! So all we have to do to find a percent of a number is to multiply.
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But how do we multiply a percent and a number together?
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Do we just forget about the percent sign and multiply the numbers together?
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No! If we did it that way, our answer would be WAY too big.
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25% should be a smaller part (or fraction) of 20 lady bugs.
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But if we did 25 times 20, we’d get 500 lady bugs!! Clearly that’s not the right answer!
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Here’s what we have to do instead...
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Remember that when you see a percent written like this with the percent sign, it’s an abbreviation for a fraction; in this case, 25 over 100.
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So we need to use that fraction form when we multiply since we’re really multiplying by a fraction.
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Now some of you may also remember that percents have a decimal form. We’ll get to that in just a minute.
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Okay then, if we use the fraction form of our percent, then our problem becomes: 25/100 times 20.
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Now that’s a problem we know how to do.
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To multiply fractions, we just multiply the top numbers, and then we multiply the bottom numbers to get the answer.
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And we can just write 20 as a fraction by putting a 1 as the bottom number, because 20 over 1 is the exact same value as 20.
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So, let’s go ahead and multiply.
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On the top, we have 25 × 20 which gives us 500.
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And on the bottom, we have 100 × 1 which is just 100.
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So our answer is 500 over 100.
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Now 500 over 100 might seem like a strange answer, but that’s just because we still need to simplify it.
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500 over 100 simplifies to 5 over 1, and 5 over 1 is just 5.
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That’s much better. So, 25% of 20 is 5.
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Alright, so to find a percent of a number, we just need to multiply the fraction form of the percent by the number and we have our answer.
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But, there’s another slightly different method that you can use that works especially well if you’re allowed to use a calculator.
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In our first percentages video, we learned that percents have both a fraction form and a decimal form.
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We’ve already seen how we can use the fraction form to find a percent of a number, but we can also use the decimal form if we want to instead.
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The procedure starts the same. If you need to find 25% of 20, you first replace the word “of” with the multiplication symbol.
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Next, we’ll replace the percent, but with its decimal form this time. 25% is the same as the decimal 0.25 Then, all we have to do is multiply.
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And although I could easily do the decimal multiplication by hand, I happen to have a calculator, so I’m gonna use it.
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I just enter 0.25 × 20, hit equals, and I get 5.
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Yep - That’s the same answer we got when we used the fraction form of 25%. Oh Yeah!
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So that’s how you find a percent of a number. You just multiply the number by either the fraction form OR the decimal form of the percent.
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Either way will give you the right answer, so you can choose whichever will be easier for you to do.
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Let’s see a couple more examples before you practice on your own.
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This next one involves money.
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Pretend that your best friend has a job walking dogs and offers to give you 35% of whatever he earns if you help walk some of the dogs.
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If your friend earns $80 that week, how much of the money will you get?
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In other words, you need to figure out what 35% of 80 is.
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Okay then, let’s start by replacing the “of” with the times symbol.
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And next we have to decide if we want to replace the percent with its fraction form or its decimal form.
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I think I’ll use the decimal form for this one which means I'll replace the 35% with 0.35 Now, all we have to do is multiply 0.35 times 80, and that’s 28.
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That means you’ll get 28 dollars if you help your friend walk those dog.
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Cha-ching! Okay then… In the last two problems, we found a percent of a number, which, like we learned at the beginning of the video, just means finding a fraction of an amount.
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And like you’d expect when finding a fraction of something, the answer was smaller than the amount we started with.
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But remember, fractions can be ‘improper’ too which means that their value is greater than 1.
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And in the same way, percents can be greater than 100%. So you might come across situations like this… Suppose that last year, your school had 400 students, but this year it has 120% of that amount.
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Well, 100% would mean the exact same number of students as last year, so 120% must mean that there’s more students now, but how many students?
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To find out, we need to calculate what 120% of 400 is.
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Great, we know just how to do that.
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We just multiply 400 by the fraction form OR the decimal form of 120%.
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Let’s use the decimal form again.
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To get the decimal form of 120%, we move the decimal point over 2 places to the left, and we get 1.20 So we multiply 1.20 times 400 which gives us 480.
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So this year there’s 480 students at school.
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Alright then, that’s how you find the percent of a number.
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And it’s a really useful math skill that has a LOT of real-life applications so it’s important to learn how to do it right.
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As always, the best way to learn math is to practice on your own.
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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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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale de niveau B1 s’appuie sur la vidéo « Math Antics - Finding A Percent Of A Number ». Les mots qui reviennent le plus souvent : percent, fraction, multiply, decimal, answer. Cette vidéo contient 78 phrases et 1225 mots à répéter en shadowing. La partie parlée dure 7:24. Le locuteur parle à un rythme naturel d’environ 165 mots par minute, proche d’une conversation courante. 87 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc facile à suivre.
Vocabulaire clé de cette vidéo
Les 15 mots les plus avancés de la vidéo, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| fraction nom | /ˈfɹæk.ʃən/ | fraction |
| multiply verbe | /ˈmʌltɪplaɪ/ | multiplier |
| decimal nom | /ˈdɛs.ɪ.məl/ | décimal, système décimal |
| bug nom | /bʌɡ/ | punaise |
| mathematics nom | /mæθ(.ə)ˈmæt.ɪks/ | mathématiques |
| multiplication nom | /ˌmʌltɪplɪˈkeɪʃən/ | multiplication |
| symbol nom | /ˈsɪmbəl/ | symbole |
| simplify verbe | /ˈsɪmplɪfaɪ/ | simplifier |
| calculator nom | /kæl.kjə.leɪ.tɚ/ | calculatrice, calculette |
| abbreviation nom | /əˌbɹi.viˈeɪ.ʃn̩/ | abréviation |
| improper adjectif | /ɪmˈpɹɑ.pɚ/ | impropre, inapproprié |
| calculation nom | /ˌkælkjuˈleɪʃn̩/ | calcul |
| calculate verbe | /ˈkælkjʊleɪt/ | calculer |
| involve verbe | /ɪnˈvɑlv/ | impliquer, involver |
| pretend verbe | /pɹəˈtɛnd/ | feindre, faire semblant |
Les verbes à particule que vous entendrez
| Mot | Prononciation | Sens |
|---|---|---|
| find out verbe | découvrir, savoir | |
| come across verbe | avoir l'air de | |
| figure out verbe | cerner | |
| go ahead verbe | /ˌɡoʊ əˈhɛd/ | vas-y, allez-y |
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Phrases conditionnelles if + proposition, will/would + verbe — une condition et son résultat | if we did 25 times 20, we'd get |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | one which means · too which means |
| Possibilité avec « might / may » might/may + verbe — quelque chose de possible mais pas certain | may also remember · might seem · might come |
| Comparatifs -er than / more … than — comparer deux éléments | smaller than · greater than |
Prononciation à surveiller
Le locuteur utilise 18 contractions et formes réduites, comme gonna, I'll, we're. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « sh » et « zh »: fraction /ˈfɹæk.ʃən/, multiplication /ˌmʌltɪplɪˈkeɪʃən/, abbreviation /əˌbɹi.viˈeɪ.ʃn̩/, calculation /ˌkælkjuˈleɪʃn̩/
- Mots longs — placez bien l’accent: mathematics /mæθ(.ə)ˈmæt.ɪks/, multiplication /ˌmʌltɪplɪˈkeɪʃən/, calculator /kæl.kjə.leɪ.tɚ/, abbreviation /əˌbɹi.viˈeɪ.ʃn̩/
Les sons difficiles pour les francophones :
- /r/ anglais — langue recourbée, sans frotter la gorge: fraction /ˈfɹæk.ʃən/, abbreviation /əˌbɹi.viˈeɪ.ʃn̩/, improper /ɪmˈpɹɑ.pɚ/, pretend /pɹəˈtɛnd/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme fraction, multiply, decimal.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.