For more information, please see full course syllabus of Basic Math

For more information, please see full course syllabus of Basic Math

## Discussion

## Study Guides

## Practice Questions

## Download Lecture Slides

## Table of Contents

## Transcription

## Related Books

### Finding a Percent of a Number

- 50% = .50
- .50 ×30

- 12% = .12
- .12 ×26

- 25% = .25
- .25 ×40

- 13% = .13
- .13 ×10

- 30% =.30
- .30 ×90

- 5% = .05
- .05 ×60

- 100% = 1
- 1 ×37

- 1% = 0.01
- 0.01 ×2500

- 40% = .40
- .40 ×35

- 20% = 0.2
- 0.2 ×15

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.

Answer

### Finding a Percent of a Number

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

- Intro 0:00
- Percent of a Number 0:06
- Translate Sentence into an Equation
- Example: 30% of 100 is What Number?
- Extra Example 1: Finding a Percent of a Number 7:12
- Extra Example 2: Finding a Percent of a Number 15:56
- Extra Example 3: Finding a Percent of a Number 19:14
- Extra Example 4: Finding a Percent of a Number 24:26

### Basic Math Online Course

### Transcription: Finding a Percent of a Number

*Welcome back to Educator.com.*0000

*For the next lesson, we are going to be finding percents of a number.*0002

*When we are finding a percent of a number, that means we are finding a portion of a number, some part of a number.*0008

*Whenever we have a percent of a number, let's translate the sentence into an equation.*0016

*Of means times; whenever you see the word of in the sentence, it means times.*0024

*Of like this is times.*0034

*When you see the word what, what means the unknown.*0036

*What is what we are looking for; that is going to be the variable.*0042

*What is the variable.*0045

*Whenever you see the word is, is means equal.*0048

*Whenever you see the word is, you are going to write that symbol.*0059

*Whenever you are finding a percent of a number, you are always going to be*0067

*multiplying the percent with the number because of is times.*0071

*Here what is a variable X; you can use whatever variable you would like.*0080

*You can use A; you can use B; you can use Z; it doesn't matter.*0085

*X is; is means equals; 30 percent.*0089

*30 percent, whenever we solve with percents, we have to change it to a decimal.*0097

*Remember we can't solve with a percent number.*0104

*Remember to change percents into a decimal, you are going to start from the end of the number.*0108

*If you don't see the decimal point, then it always belongs at the end of a number.*0122

*You are going to move two spaces to the left.*0128

*You know it is going to be to the left when you change it to a decimal because decimals are small.*0132

*Think of decimals as smaller than percents.*0136

*To change from a percent to a decimal, we are going to move the decimal point*0140

*over to the left because that is going to make the number smaller.*0144

*Two spaces; it is going to go one, two.*0147

*That is where the decimal point is going to go.*0152

*Here it is going to be 0.30; this is going to change to 0.30.*0156

*Of always means times.*0164

*Here I want to show that I am going to multiply this number to this number.*0171

*Be careful because we don't want to use X for times anymore because here we have X as a variable.*0176

*Instead of using X, use parentheses.*0184

*You also probably know about the dot as times; sometimes that is OK.*0190

*But between two numbers, you don't want to use dot because that looks like a decimal also.*0195

*Maybe if you write it a little bit too low, it might look like a decimal.*0201

*Whenever you are going to multiply two numbers together, it is always best to just use parentheses.*0207

*Writing the number in parentheses like that between two numbers,*0215

*it shows that you are going to be multiplying those two.*0219

*What is 30 percent of 100?*0224

*You know that you are going to be multiplying 0.30 with 100 to find the missing value X.*0225

*100 times 0.30 is going to be 0; then 0; 0; I'm sorry.*0235

*If you want to just multiply this 0 out, you can do that.*0250

*Then multiply this through under; put a 0 here; 3 times 0; 0; 3.*0254

*3; 0; 0; 0; be careful when you have so many 0s.*0264

*Within the problem, because we multiplied, how many numbers are behind the decimal point?*0269

*There is two numbers; one, two; we have two numbers behind the decimal point.*0274

*You are going to go to the answer starting at the end.*0279

*You are going to go one, two.*0284

*That is where the decimal point is going to go; 30.*0286

*X equals... all this was 30; there is a shortcut.*0291

*Whenever you multiply a decimal number, to a multiple of 10... that is 10, 100, 1000, 10000.*0296

*Whenever you have a number multiplied to a number with 1*0306

*and then 0s like 100, there is a shortcut way of doing this.*0311

*You can count how many 0s there are in that number; 100 has two zeros.*0316

*Then you are going to move this decimal point two spaces.*0324

*You know, since you are going to be multiplying, when you multiply, the number tends to get bigger.*0331

*You are going to go two spaces to the right*0337

*because moving the decimal point over to the right makes the number bigger.*0340

*You are going to one, two; that is going to give you 30.*0344

*Remember if you don't see a decimal point, it is always at the end right there.*0348

*If you were multiplying this number by 10, let's say you are multiplying it by 10.*0356

*10 has only one 0.*0363

*You would only move the decimal point over once to the right.*0366

*That would be 3.0 which is the same thing as 3.*0371

*Remember if there is a 0 at the end of a number behind the decimal point, it is as if it is not there.*0374

*3.0 is the same thing as 3.*0379

*If you are multiplying by 1000, 1000 has three 0s.*0388

*You would have to move the decimal point over three spaces.*0394

*Remember if you have an empty space, you have to fill it in with an extra 0.*0398

*That is the shortcut when multiplying by a number that is a multiple of 10; 10, 100, 1000, and so on.*0404

*You just have to count the number of 0s and then move the decimal point over that many spaces.*0413

*What is 30 percent of 100?--that is 30; 30 is 30 percent of 100.*0420

*We are just going to do a few more examples.*0433

*Here 50 percent of 18 is... here 50 percent.*0435

*Again remember whenever we have to solve using percents,*0443

*we have to change it to a decimal because you can't solve with a percent.*0448

*If you have a percent, then you need to change it to a decimal.*0453

*Remember percent to decimal.*0458

*If we have a percent, 50 percent, you want to move the decimal point*0466

*over two spaces between percent to decimal or decimal to percent.*0471

*From percent to decimal, you start at the end right here.*0479

*You have to move two spaces to the left because remember decimals are small numbers.*0484

*You want to turn this number into a smaller number.*0488

*To do that, you have to move the decimal point over to the left.*0492

*If you move it to the right, then the number gets bigger.*0496

*So move it to the side that is going to make it smaller.*0499

*Two spaces, it is going to be right here.*0504

*One, two; drop the percent sign; becomes 0.50.*0506

*Or because this 0 is at the end of a number behind the decimal point, it is as if it is not there.*0512

*You don't even have to write it.*0519

*0.50 is the same thing as 0.5; it is the same thing.*0520

*This is 0.50 or 0.5; of means times.*0528

*Remember if I am going to multiply two numbers together, I want to write it in parentheses.*0535

*Times 18 is; is is equals; then the number X which is what we are solving for.*0538

*As long as you know that you have to multiply the percent with the number,*0554

*because of is between the two numbers, again 50 percent you change to a decimal.*0560

*As long as you know that you have to multiply these two, you don't have to write it into this equation*0565

*because all we are doing is finding percents of a number; of meaning times.*0573

*You just have to be able to multiply these two numbers together.*0579

*The reason why I am saying write an equation is because for the next lesson,*0582

*we are going to have to solve for maybe this number or solve for the percent.*0589

*This number will be given to you.*0598

*In that case, when you are solving for another number,*0600

*this is the easiest way for you to be able to write an equation*0603

*and know what your variable is, what it is you are solving for,*0608

*because a variable is always what you are solving for.*0611

*If you don't want to do it this way, then just make sure you remember to multiply.*0616

*Of means times; you are going to be multiplying the number with the other number.*0622

*0.5 times 18; I am going to write that here; 18 times 0.5.*0631

*8 times 5 is 40; 5 times 1 is 5; plus 4 is 9.*0640

*Within here, how many numbers are behind the decimal point?*0648

*I only have one; starting right here, you are going to go inwards one.*0650

*My answer is going to be 9.0 or 9.*0657

*9.0 and 9 is the same thing.*0663

*Again 0 is at the end of a number behind the decimal point so you can just drop it; 9.*0666

*50 percent of 18 is 9; 50 percent means half.*0673

*50 percent means half; what is half of 18?*0679

*Half of 18 is 9 meaning if you had let's say 18 pieces of candy.*0684

*You had to split it in half; you can only take half of them.*0690

*You take half; your brother or sister has to take the other half.*0695

*Then you would take 9; your brother or sister would take the other 9.*0699

*50 percent means half.*0704

*All you have to do is 50 percent of 18, you just figure out what half of 18 is.*0705

*The next one, here 8 percent; from percent to a decimal.*0712

*Again you are going to start right here.*0723

*You are going to move two spaces to the left.*0724

*You are going to go one and two.*0727

*Point... there is an empty space right here.*0731

*You have to fill it with a 0; 0; 8.*0735

*Then again you are going to drop the percent because it is no longer a percent.*0740

*0.08; 8 percent is 0.08; of means times; 6.*0743

*Again write it in parentheses when you are multiplying two numbers.*0752

*Is equals the number X or blank.*0759

*0.08 times 6; 0.08 times 6; 8 times 6 is 48; this is just 0.*0764

*How many numbers do I have behind the decimal point?*0785

*I only have two; there is none right here.*0789

*Decimal point is at the end right here; I only have two.*0791

*From the end, I am going to go in two spaces; one, two; right there.*0795

*8 percent of 6 is 0.48.*0803

*The next one, 99 percent of 100 is.*0815

*99 percent changes to a decimal because you are solving with it; 99 percent.*0819

*You are going to go one, two; it is going to be 0.99.*0826

*Of means times; 100 in parentheses; equals something; 0.99 times 100.*0836

*Let's do our shortcut; remember if you want, you can multiply it out like this.*0846

*Remember whenever you multiply a number that is a multiple of 10, meaning 10, 100.*0852

*Or I'm sorry; not a multiple of 100; but if you have a power of 100; 10, 100, 1000, and so on.*0859

*What that means is any number with a 1 with a bunch of 0s; 10, 100, 1000, 10000, and so on.*0866

*Since I have 100 and 100 has two 0s, I am going to take the decimal point.*0878

*I am going to move it two spaces.*0887

*But remember I have to move it to the right two spaces*0889

*because when you multiply by 100, that means your number has to get bigger.*0892

*To make this number bigger, I am going to move it to the right.*0897

*One, two; that is where my decimal place is going to go.*0900

*That is going to be 99.0.*0904

*Or remember if it is at the end of a number, you can just drop it.*0909

*You can make it invisible; 99; 99 percent of 100 is 99.*0914

*Whenever you find a percent of 100, it is always just that number.*0921

*If I have 1 percent of 100, that is going to be 1.*0925

*If I have 2 percent of 100, that is going to be 2.*0931

*If I have 100 percent of 100, that is going to be 100.*0935

*Whenever you take a percent of 100, it is just going to be this number without the percent sign.*0938

*68 percent of 100 is 68; that is only if this number is 100.*0945

*Let's just do a few more; what is 25 percent of 60?*0958

*This is what we are solving for; I can make that into my variable.*0966

*Use a question mark; you can do a little blank; is equals.*0971

*25 percent; percent to decimal; I am going to change 25 percent.*0980

*Start right here at the end; you are going to go in one, two.*0993

*It is going to be 0.25; of means times.*0997

*Again since you are multiplying two numbers together,*1007

*you are going to write it in parentheses like that.*1009

*To solve this, I have to... to find the what, to find this, I have to multiply 0.25 with 60.*1011

*60 times 0.25; this is 0; 6 times 5 is 30; put a 0 here.*1023

*2 times 0 is 0; 2 times 6 is 12.*1035

*Add them together; 0; 0; 5; 1.*1043

*How many numbers are behind decimal points?--I only have one, two.*1049

*You are going to start here; you are going to go one, two.*1056

*Remember 0s are at the end of a number behind the decimal point.*1060

*This is just going to be 15; X, this unknown, is 15.*1063

*That means 15 is 25 percent of 60.*1069

*What number is 10 percent of 10?*1078

*Again what number is the same thing as just what or blank or question mark.*1081

*You are looking for the number.*1087

*Is 10 percent; one, two; 0.10; of 10.*1089

*I know that 10 times 10 is 100.*1107

*You can just move the decimal point over that many times.*1111

*Or we can just use our shortcut.*1113

*Since I am multiplying a decimal by 10, how many 0s do I have in 10?*1116

*I only have one 0.*1121

*I am going to move this decimal point over one time.*1124

*It is going to be 1.0; but that is the same thing as 1.*1128

*You can just drop this 0.*1136

*If the decimal place is at the end of a number, then you can just make that invisible.*1139

*You can just write that as 1; that means 1 is 10 percent of 10.*1145

*Find 5 percent of 40; we want to find 5 percent of 40.*1156

*5 percent; this right here is the same thing as this.*1162

*We still have to change this; be careful.*1168

*Just because you don't see the percent sign doesn't mean that you can just drop this number down.*1171

*It is still a percent; you have to change this to a decimal.*1176

*5 percent; again start at the end; you are going to go one, two.*1189

*Going to be point, space right here, 0, 5; of is times; 40.*1196

*You are going to multiply these two numbers together; 0.05 times 40.*1212

*0 times 5 is 0; 0 times 0 is 0; put a 0 down there.*1220

*4 times 5 is 20; 4 times 0 is 0; add the 2.*1229

*Be 0, 0; remember we are adding them down; 200.*1239

*How many numbers total are behind decimal points?--I only have two; these two.*1245

*I am going to go from here; I am going to go one, two; in two spaces.*1251

*My answer is 2.00 which is remember the same thing as just 2.*1258

*My answer is going to be 2; 5 percent of 40 is 2.*1265

*100 percent of 18; 100 percent of 18.*1276

*When I say 100 percent, I am trying to say all of it.*1282

*This is like saying all of 18; 100 percent of 18 is all of 18.*1289

*What is all of 18?*1295

*All of 18, if you have 18 pieces of candy, what is all of it?*1297

*How many would be considered all of it?--18.*1301

*100 percent of 18 is just 18.*1304

*If you want to just solve it out, 100 percent into a decimal is going to be one, two, 1.0.*1308

*Or remember this is the same thing as 1.*1318

*Even though you don't see a decimal here, numbers always have a decimal point.*1323

*It is just if you don't see it, if it is invisible, it is always at the end.*1329

*100 percent is the same thing as 1 in decimal.*1334

*It is like saying 1, or 1.0 if you want, times 18.*1338

*What is 1 times 18?--isn't that 18?*1346

*Again shortcut, if you have 100 percent, you are saying what is all of it?*1352

*All of 18 is 18.*1357

*1 percent of 2000; into a decimal.*1361

*Right here, you are going to go one, two; the decimal point.*1372

*Empty space; you are going to fill it in with a 0; and 1.*1378

*1 percent in decimal is 0.01; be careful that you don't just make it 0.1.*1383

*Of, times; 2000; multiply it out; times 0.01; this is 0; 0; 0; 2.*1392

*Then this is just all 0s so I don't have to write that in.*1414

*It is like adding 0s.*1418

*If I add 0s to this number, it is just going to be that same number.*1419

*From here, how many numbers are behind decimal points?--two.*1426

*Start from here; you are going to go one, two, decimal point.*1430

*My answer here is going to be 20.00.*1435

*Again if the 0s are behind the decimal point at the end of a number, you can just drop them.*1446

*I can drop this, drop this; it will be 20 point.*1450

*But then I can just drop that, make that decimal point invisible if it is at the end.*1454

*It will just be 20.*1458

*The final example, a bag of candy contains 40 pieces.*1467

*If Susanna ate 20 percent of the candy or everything in the bag of candy, how many pieces did she eat?*1475

*A whole bag contains 40 pieces; she ate 20 percent of it.*1487

*How many pieces did she eat?--look at this; 20 percent of the candy.*1491

*What is the candy?--how many pieces does the bag of candy contain?--40 pieces.*1504

*It is like saying she ate 20 percent of the 40 pieces.*1510

*20 percent, again if I want to solve with this number, I have to change it to a decimal.*1516

*20 percent to decimal; I am going to start here; go one, two; is 0.20.*1523

*Of is times; you are going to multiply what?*1537

*The 40 because she ate 20 percent of all the pieces; times 40.*1541

*Here thing is going to be...*1554

*Remember if the 0 is at the end of a number and it is behind the decimal point, I can just drop it.*1557

*This is the same thing as 0.2 times 40.*1562

*I can't drop this 0; be careful here.*1566

*Don't drop the 0 because this 0 is not behind the decimal point.*1569

*Decimal point is right here; right there.*1574

*Since it is not behind the decimal point, I can't drop the 0.*1579

*But this one, I can; that will just make it easier to multiply.*1583

*40 times 0.2 is going to be 80.*1587

*I only have one number behind the decimal point.*1595

*Start here; you are going to go in one space.*1598

*0.2 times 40 is going to be 8.*1601

*Good thing with word problems is that you can estimate if your answer sounds correct.*1607

*Let's say I forget to count how many numbers I have behind decimal points and I just leave it as 80.*1613

*80 can't be my answer because if the bag of candy contains only 40 pieces, Susanna ate 20 percent of it.*1620

*Would it make sense if my answer was 80, that she ate 80 pieces?*1631

*There is only 40 pieces; I know this answer sounds correct.*1637

*It seems correct; it seems reasonable; remember 50 percent is half.*1646

*If Susanna ate 100 percent of the candy, that means she would have eaten all of the candy.*1653

*Then my answer would just be 40.*1658

*If Susanna ate 50 percent of the candy, remember 50 percent is half of the number.*1661

*If this said 50 percent, then you would have to just find half of 40.*1671

*She would have eaten 20 pieces of candy.*1676

*She only ate 20 percent; that means she has to have eaten less than half.*1680

*If 20 is half, we know 8 is reasonable then because it has to be less than half.*1685

*That is it for this lesson; thank you for watching Educator.com.*1695

0 answers

Post by sherman boey on July 28, 2014

why 2 numbers need ()? cant i just replace it with X?

0 answers

Post by CW Burnette on February 8, 2013

i get it but is there another short cut