Shadowing Practice: Math Antics - Calculating Percent Change - Learn English Speaking with Video
בחר מצב תרגול
כל מצב פותח חדר תרגול במסך מלא.
150 משפטים
אם המשפטים קצרים או ארוכים מדי, לחץ על ערוך כדי להתאים אותם.
1
So, with a customer acquisition cost of $35 ,000, and a weighted sales pipeline of $1 .2 ,000, and a monthly recurring revenue of $2 .4 million,
2
we had net sales go from 4 .9 million APR to approximately 5 .1 million per capita.
3
But what about the percent change?
4
Ah, yes, percent change.
5
It's always good to know percent change.
6
I'll explain that all to you right now.
7
Oh, sorry, I'm getting a phone call.
8
I got to take this, but then I'll explain all that percent change to you.
9
Hi, I'm Rob.
10
Welcome to Math Antics.
11
In this lesson, we're going to learn how to calculate percent increase and decrease, known collectively as percent change.
12
If you're not very familiar with percents, I'd highly recommend watching some of our other videos about them before continuing on.
13
Lots of times, when you have a change in value, you just say how much something goes up or down in absolute terms,
14
like: "The population of this city increased by a thousand people." or the cost of this shirt decreased by $15.
15
But you can also express those sorts of changes in relative terms using percentages.
16
Unlike an absolute change, a percent change always relates the amount of change to the number 100.
17
The term 'percent' literally means 'per 100'.
18
So 'percent change' means 'per 100 change' or the change 'per 100'.
19
So let's start by imagining that you have 100 of something.
20
Like 100 bucks.
21
Oh yeah!
22
If you start out with 100, but then you get 20 more, that would be a 20 % increase, because the amount went up by 20 per the original 100.
23
Likewise, if you start out with exactly 100 bucks but then you lose 15, that would be a 15 % decrease because it went down by 15 per the original 100.
24
So as you can see, it's pretty easy to figure out the percent change when the original amount is exactly 100.
25
But you don't have to start with 100 to express change as a percentage.
26
Almost any original value and any amount of change can be represented as a percent change thanks to equivalent fractions.
27
For example, instead of $100, suppose that you start out with $750.
28
Then imagine that you get $150 more.
29
What percent increase is that?
30
To figure that out, let's use a simple diagram.
31
This blue bar represents the original $750.
32
And this green bar represents the $150 increase.
33
Now let's use our imagination and ask, "What if that original amount was only $100?" what would the equivalent change in value be?
34
Basically, we're asking: If you had the fraction 150 over 750,
35
what would an equivalent fraction be that has 100 as the bottom number?
36
Put another way, if you have 750 and get 150 more, it's equivalent to having 100 and getting 'x' more.
37
We're using the letter 'x' to temporarily represent the missing value.
38
The top number of the original fraction is the absolute change.
39
and the top number of the equivalent fraction is the percent change.
40
So let's figure out what the missing value is in two different ways.
41
First, visually using our diagram, and second, using simple arithmetic.
42
By definition, if you divide any amount up into 10 equal parts, then each one of those parts will be 10 % of the original amount.
43
So, if you divided the original $750 up into 10 equal amounts, Each of those amounts would be $75.
44
That means that a $75 increase would be equivalent to a 10 % increase.
45
Of course, we had an increase of $150, not $75.
46
150 is exactly 75 plus 75, so that would be another 10 % of the original amount.
47
As you can see from the diagram, if you start with 750 and then you get 150 more, that's equivalent to starting with 100 and getting 20 more.
48
In other words, it's a 20 % increase.
49
Now let's see how we could get that same answer without using a diagram.
50
Using a little basic algebra, we can solve for the unknown value x, All we need to do is multiply both sides of the equation by 100.
51
Doing that gives us x all by itself on this side of the equation because the 100 over 100 cancels out.
52
And on the other side, we have the change in value divided by the original value all times 100.
53
Using a calculator, 150 divided by 750 equals 0 .2 and 0 .2 times 100 equals 20,
54
or 20 percent, which is the exact same answer we got from our diagram.
55
So the formula for calculating percent change is simple:
56
All you have to do is take the absolute change and divide that by the original amount, and then multiply the result by 100.
57
This formula may look even more intuitive to you if we put it back in the equivalent fraction form.
58
These are just two different ways of writing the exact same relationship.
59
Now that we have a formula for calculating percent change, let's try using it in a couple quick examples.
60
Suppose a doggy daycare takes care of 25 dogs on Friday, but on Saturday, three more dogs join the group.
61
What percent increase is that?
62
Well, the original amount of dogs is 25 and the change in dogs is +3.
63
According to our formula, we just need to divide the change by the original
64
and multiply it by 100 to get the percent change.
65
Using a calculator, we get 3 divided by 25 equals 0 .12.
66
and then 0 .12 times 100 equals 12.
67
That means the number of dogs at the daycare increased by 12 % from Friday to Saturday.
68
That was pretty easy, but what about this example?
69
Suppose you want to buy a pair of shoes that cost $65.
70
but you have a discount coupon that will reduce the price by $15.
71
What would the percent decrease in price be if you use your coupon?
72
Well, the original price is $65 and the change in price will be -15.
73
It's negative because it's a decrease.
74
So let's plug those numbers into our formula.
75
That gives us percent change equals negative 15 divided by 65 times 100.
76
Again, using a calculator, negative 15 divided by 65 equals negative 0 .23 rounded off to two decimal places.
77
And negative 0 .23 times 100 equals negative 23.
78
so the coupon will decrease the price of the shoes by 23%.
79
Okay, so if you're given an original amount and told how much that amount changes, it's really easy to calculate the percent change using this simple formula.
80
But sometimes math problems don't tell you what the absolute change in a value is.
81
Instead, they just give you an original value and a new value.
82
In that case, you need to calculate the change yourself.
83
Here's how you do that: Suppose you're given a problem that says last year your school had 420 students, but this year it has 441 students.
84
What's the percent change in student population?
85
This problem doesn't directly say what the absolute change in student population was.
86
It just tells us what the value was originally and what it is now.
87
We know that there was a change because of the difference in the numbers.
88
And in math, what does the word "difference" make you think of?
89
Yep, subtraction.
90
We can figure out the absolute change just by subtracting.
91
But order matters in subtraction.
92
So should we subtract the original amount from the new amount or the new amount from the original amount?
93
Well, the standard way of doing it is to start with the new amount and subtract the original amount from it.
94
If the new amount is bigger than the original, the answer you get will be a positive number.
95
which means that you have a percent increase.
96
But if the new amount is smaller than the original, the answer you get will be a negative number, which means you have a percent decrease.
97
So if we do that, we have 441 minus 420, which is positive 21.
98
So we have an increase of 21 students.
99
Positive 21 divided by the original amount, 420, equals positive 0 .05.
100
and 0 .05 times 100 equals 5.
101
Since that's positive, we have a 5 % increase in students.
102
But what if you subtracted in the wrong order and got negative 21 instead?
103
If you plug that into the formula for percent change, you'll get -21 divided by 420 which equals -0 .05.
104
and then multiplying by 100 gives you -5, which suggests a 5 % decrease because the sign is negative.
105
But, since you're paying attention, you'll realize that you couldn't possibly have a 5 % decrease in students since the number got bigger over time.
106
The problem tells us that it was 420 last year and this year it's 441.
107
So you must really have a 5 % increase.
108
The point here is that in math, it's always important to use your intuition and ask yourself if an answer makes sense,
109
rather than simply trying to memorize a formula without thinking about what it really means.
110
And speaking of intuition, before we wrap up, I want to explore just a few more situations that will hopefully give you a better intuition about percent increase and decrease.
111
First, let's consider the case where you start with 1 of something and end up with 2.
112
What would the percent increase be?
113
Well, the original amount is 1, and the change is also 1.
114
Plugging those numbers into the formula gives 1 over 1 times 100, which simplifies to 100.
115
So the percent increase is 100%.
116
That may seem kind of odd, but it makes total sense if you think about it.
117
If you have 1 and then you get 1 more, you're gaining 100 % of what you started with.
118
And that's true any time the original amount doubles.
119
If you start with 2 and get 2 more, for a total of 4, the increase is 100 % because 2 divided by 2 times 100 is 100.
120
And if you start with 5 and then get 5 more, for a total of 10, The increase is 100%.
121
because 5 divided by 5 times 100 is also 100.
122
So anytime the original amount you have doubles, it's an increase of 100%.
123
But what if you start with 2 and then end up with 1?
124
Considering what we just learned, you might be tempted to think that that's a decrease of 100%.
125
But if we use our formula, we'll see that that's not the case.
126
Since the original amount is 2, we put a 2 on the bottom of the fraction.
127
and the change is -1 since we decreased from 2 to 1.
128
So a negative 1 goes up on top.
129
Now, if we simplify, we get negative 1 divided by 2, which is negative 0 .5.
130
and negative 0 .5 times 100 is negative 50 or a 50 % decrease.
131
The reason that the percent changes are different in these two cases, doubling the amount versus cutting it in half, is that the percent change always compares the change to the original amounts,
132
which are different in these two cases.
133
Finally, let's determine what the percent increase would be if you start with 1 and end up with 3.
134
And conversely, what would the percent decrease be if you start with 3 and end up with 1?
135
In the first case, the change is positive 2 and in the second case, it's negative 2.
136
Let's plug those values into our formula for percent change, along with the original values in each case, and see what answers we get.
137
Going from 1 to 3, positive 2 divided by 1 times 100 equals 200, or a 200 % increase.
138
And, going from 3 to 1, -2 divided by 3 times 100 equals -67, rounded to the nearest whole number,
139
or a 67 % decrease.
140
Again, even though the magnitude of the change was the same, the percent changes are different because we started out with different original amounts.
141
And this example also shows that you can get a percent change that's greater than 100%.
142
Alright, so now you know what percent change is and how to calculate it.
143
The formula for calculating it is pretty simple, so you should be able to remember it after you've used it on several problems.
144
And that's the key to learning math.
145
You can't just watch videos about it.
146
You need to actually use it to solve problems.
147
So, be sure to practice what you've learned in this video!
148
As always, thanks for watching Math Antics, and I'll see you next time!
149
That's what my calculator says.
150
Learn more at MathAntics .com.
הורד אפליקציה
כל מה שאתה צריך כדי לדבר בשטף
הגיית AIציון לכל משפט
תרגול IPAשלוט בכל צליל
אוצר מיליםבנה את מאגר המילים שלך
משחק אוצר מיליםלמד תוך כדי משחק
אותו ערוץ
B2Extras ArcLength YouTube
American AccentHigh School StudentsUniversity Students
B1Math Antics - Finding A Percent Of A Number
American AccentKidsTeensHigh School Students
B14
Math Antics - Negative Numbers
American AccentKidsDaily Conversation
B1Math Antics - Percents Missing Total
American AccentHigh School Students
B1Math Antics - What Percent Is It?
American AccentDaily ConversationHigh School StudentsUniversity Students
B1Math Antics - Percents And Equivalent Fractions
American AccentDaily ConversationHigh School StudentsUniversity Students
B1Math Antics - What Are Percentages?
American AccentHigh School StudentsUniversity Students
FOR YOU
המלץ על סרטון
B112
205 משפטים
Let's talk about Money in English
American AccentBusiness EnglishTravel EnglishDaily Conversation
B11
13 משפטים
English in a Minute: Change of Heart
American AccentDaily ConversationHigh School StudentsUniversity Students
B1131 משפטים
Adding Fractions With Unlike Denominators
American AccentHigh School StudentsUniversity Students
B23
132 משפטים
How to Actually Get Better at Physics
Business EnglishHigh School StudentsUniversity Students
B12
92 משפטים
Introduction to interest | Interest and debt | Finance & Capital Markets | Khan Academy
American AccentBusiness EnglishUniversity StudentsWorking Adults
B11
278 משפטים
How to read ALL NUMBERS in English - BIG NUMBERS, Decimals, Dates, Fractions, Phones, Ordinals
British AccentBusiness EnglishDaily ConversationHigh School Students
B18
338 משפטים
You Understand English But Can't Speak — The Real Reason Nobody Explains
American AccentBusiness EnglishDaily ConversationUniversity Students
A230 משפטים
Top Notch 1 Unit 10 Scene 2
Business EnglishTeensDaily Conversation
B26
109 משפטים
Carnival Scam Science (and how to WIN)
American AccentBusiness EnglishUniversity StudentsWorking Adults
B21
16 משפטים
English in a Minute: Break Even
American AccentBusiness EnglishUniversity StudentsWorking Adults
C11
99 משפטים
Financial ratio analysis
Business EnglishUniversity Students
אוצר מילים והערות הגייה לשיעור הזה
שיעור הדיבור הזה ברמה B1 מבוסס על הסרטון “Math Antics - Calculating Percent Change”. המילים שחוזרות הכי הרבה: percent, amount, original, increase, negative. בסרטון הזה יש 150 משפטים ו-1924 מילים לתרגול Shadowing. הדיבור נמשך 12:50. הדובר מדבר בקצב טבעי של כ-150 מילים בדקה, קרוב לשיחה יומיומית. 88% מהמילים נמצאות בין 3,000 המילים הנפוצות ביותר באנגלית, כך שקל לעקוב אחרי אוצר המילים.
אוצר מילים מרכזי בסרטון הזה
15 המילים המתקדמות ביותר בסרטון, עם ההגייה והמשמעות שלהן:
| מילה | הגייה | משמעות |
|---|---|---|
| divide פועל | /dɪˈvaɪd/ | חילק, פיצל |
| decrease פועל | /dɪˈkɹiːs/ | פחת |
| calculate פועל | /ˈkælkjʊleɪt/ | חישב \ חִשֵּׁב |
| fraction שם עצם | /ˈfɹæk.ʃən/ | חלק |
| mathematics שם עצם | /mæθ(.ə)ˈmæt.ɪks/ | מָתֵמָטִיקָה |
| diagram שם עצם | /ˈdaɪ.ə.ɡɹæm/ | תַּרְשִׁים |
| calculator שם עצם | /kæl.kjə.leɪ.tɚ/ | מַחְשְׁבוֹן, מונה |
| plug שם עצם | /plʌɡ/ | תֶּקַע |
| buck שם עצם | /ˈbʌk/ | אַיָּל |
| equation שם עצם | /ɪˈkweɪ.ʒən/ | משוואה \ מִשְׁוָאָה |
| shoe שם עצם | /ˈʃu/ | נַעַל |
| arithmetic שם עצם | /æɹɪθˈmɛtɪk/ | חֶשְׁבּוֹן |
| memorize פועל | /ˈmɛm.əˌɹaɪ̯z/ | שִׁנֵּן |
| intuitive שם תואר | /ɪnˈtjuːɪtɪv/ | אינטואיטיבי |
| algebra שם עצם | /ˈæl.d͡ʒɪ.bɹə/ | אַלגֶבּרָה |
Phrasal verbs שתשמעו
| מילה | משמעות |
|---|---|
| figure out פועל | הֵבִין, מצא תשובה |
| go up פועל | עָלָה |
| go down פועל | ירד |
משפטים שכדאי לחזור עליהם
משפטים קצרים ושלמים מהסרטון שאפשר להשתמש בהם בשיחה יומיומית:
- I'll explain that all to you right now.
- To figure that out, let's use a simple diagram.
- What's the percent change in student population?
- You can't just watch videos about it.
- That's what my calculator says.
דקדוק בסרטון הזה
המבנים שהדובר משתמש בהם הכי הרבה, עם המילים המדויקות מהסרטון:
| מבנה | בסרטון |
|---|---|
| משפטי תנאי (Conditional sentences) if + clause, will/would + verb — תנאי ותוצאה שלו | if we use our formula, we'll see |
| הווה מושלם (Present perfect) have/has + past participle — פעולה שקרתה בעבר ועדיין יש לה חשיבות או השפעה עכשיו | you've used · you've learned |
| סביל (Passive voice) be + past participle — הדגש הוא על מה שקורה, לא על מי שעושה את הפעולה | can be represented · might be tempted |
| משפטי זיקה (Relative clauses) who / which + clause — מידע נוסף על אדם או דבר | percent, which is · number, which means |
הגייה ששווה לשים לב אליה
הדובר משתמש ב-24 קיצורים וצורות מקוצרות, כמו you're, I'll, we're. אמרו אותם בצורה הקצרה, כפי שאתם שומעים אותם.
- הצלילים של “th”: mathematics /mæθ(.ə)ˈmæt.ɪks/, arithmetic /æɹɪθˈmɛtɪk/
- הצלילים של “sh” ו-“zh”: fraction /ˈfɹæk.ʃən/, intuition /ˌɪn.tjuːˈɪʃ.ən/, subtraction /səbˈtɹækʃən/, equation /ɪˈkweɪ.ʒən/, shoe /ˈʃu/
- מילים ארוכות — שימו לב להטעמה: mathematics /mæθ(.ə)ˈmæt.ɪks/, calculator /kæl.kjə.leɪ.tɚ/, intuition /ˌɪn.tjuːˈɪʃ.ən/, arithmetic /æɹɪθˈmɛtɪk/, intuitive /ɪnˈtjuːɪtɪv/
צלילים שדוברי עברית מתקשים בהם:
- /w/ — שפתיים מעוגלות, לא /v/: equation /ɪˈkweɪ.ʒən/, likewise /ˈlaɪkˌwaɪz/, acquisition /ˌæk.wɪˈzɪʃ.ən/
- /æ/ — פתוח יותר מה-“אֶ” העברית, לא כמו “a” ב-“cup”: calculate /ˈkælkjʊleɪt/, fraction /ˈfɹæk.ʃən/, mathematics /mæθ(.ə)ˈmæt.ɪks/, diagram /ˈdaɪ.ə.ɡɹæm/, subtract /səbˈtɹækt/
- /r/ — הלשון לא נוגעת בשום מקום, לא ה-“ר” הגרונית: decrease /dɪˈkɹiːs/, fraction /ˈfɹæk.ʃən/, diagram /ˈdaɪ.ə.ɡɹæm/, subtract /səbˈtɹækt/, daycare /ˈdeɪkeə(ɹ)/
איך לתרגל עם הסרטון הזה
- הקשיבו לכל הסרטון פעם אחת בלי לדבר, ורשמו את המילים שאתם לא מכירים.
- התחילו במהירות 0.75×, תרגלו Shadowing משפט אחר משפט, וחזרו למהירות רגילה כשזה מרגיש קל.
- הקליטו את עצמכם והשוו למקור, תוך תשומת לב למילים כמו divide, decrease, calculate.
מהי טכניקת השאדואינג?
שאדואינג היא טכניקת למידת שפה מבוססת מדע שפותחה במקור להכשרת מתורגמנים מקצועיים ופופולרית על ידי הפוליגלוט ד"ר אלכסנדר ארגואלס. השיטה פשוטה אך עוצמתית: אתה מקשיב לאודיו באנגלית ילידית וחוזר עליו בקול רם מיד — כמו צל העוקב אחרי הדובר עם עיכוב של 1–2 שניות בלבד. בניגוד להאזנה פסיבית או תרגילי דקדוק, שאדואינג מכריח את המוח והשרירים בפה לעבד ולשחזר דפוסי דיבור אמיתיים בו זמנית. מחקרים מראים שזה משפר משמעותית את דיוק ההגייה, האינטונציה, הקצב, הדיבור המחובר, הבנת השמיעה ושטף הדיבור — מה שהופך אותו לאחת השיטות היעילות ביותר להכנה לIELTS Speaking ולתקשורת באנגלית בעולם האמיתי.