How to Find The LCD (Lowest Common Denominator) The EASY WAY

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Жыл бұрын

How to Find The LCD (Lowest Common Denominator).
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Пікірлер: 105

@CapitalWorksPro Жыл бұрын

From a mathematician (not me) Find a number that your denominators share in common. 20 and 32 share the number 2 in common. 20 ÷ 2 is 10 32 ÷ 2 is 16 10 and 16 also share 2 in common. 10 ÷ 2 is 5 16 ÷ 2 is 8 5 and 8 share 1 in common. Once we get to 1 in common, we stop and multiply all of the numbers on the outside that we found in common, and the last two numbers. Visual aid below to show what we did. 2 |20 & 32 ------------- 2 | 10 & 16 ------------- 1 | 5 & 8 2 * 2 * 1 * 5 * 8 = LCD = 160 You'll notice that 20 and 32 also share 4 in common. 20 ÷ 4 is 5 32 ÷ 4 is 8 4 * 1 * 5 * 8 = 160 So long as both denominators actually have the number you choose in common with each other, this will work.

@yuretenno1 Ай бұрын

🤯🤯🤯 simple and efficient

@EY02 6 ай бұрын

When you got to the part where you speak about the LCD Prime Factors, adding exponents, really complicated things. Your comment section is filled with much better suggestions on the easiest steps as your tutorial over complicated things and made me just as confused as I was before.

@tonywright560 Жыл бұрын

I've said in response to some of your other videos that if I was ever taught your method of using the factor tree to find a LCD, which I doubt, I have forgotten it. This video was excellent. I actually recorded it so that I can review. Maybe it was not a profoundly important mathematical method but I believe it will help me understand other things as I relearn maths. Thank you.

@spudhead169 Жыл бұрын

If you want to skip all the crud he's spouting at the start, jump to 6:27

@Kobe_Abogutal Жыл бұрын

he's like that every video tbh

@lauriejerome9179 Жыл бұрын

It's aggravating, isn't it!

@spudhead169 Жыл бұрын

@@lauriejerome9179 I can understand him giving some context for kids who are new to all this. I just feel that six and a half minutes of it is a tad excessive. So yes, it is quite vexing. Especially when there's videos of people solving Calc III integrals in less time than his intro took.

@ryanburnham1932 Жыл бұрын

When there is only two fractions, I always just multiply the denominators together, and multiply the numerators by the other denominator. You get a common denominator this way, which is all you need to add/subtract (not the LCD itself as you stated), of course this does lead to reducing the resulting fraction, if you so choose (again no real need as you still have the correct answer but it may be beneficial). Of course if you have several fractions with different denominators, say 10, it may be in your interest to have a "trick" to find the LCD, however you stated this works for trying to find it between two denominators and when I tried it with 5 different denominators I was off by a factor of almost 10. I did still get a common denominator and was able to add them but it wasn't the LCD. My point is that why take all these extra steps and encourage students to take these extra steps early instead of just at the end, reducing a fraction seems like there is less opportunity for error than the process you provided. K.I.S.S. = Keep it Simple Stupid a method I like to use from getting myself in trouble algebraically, or life in general.

@KRYPTOS_K5 Жыл бұрын

Yes. I also perceived your point before your claim. It is very interesting as a theory of factors and primes and other issues. It can also be used to reduce fractions in order to operate them together however to present it like "mmc" (lcm) to fundamental students as a practical method is another issue... Brasil

@tonywright560 Жыл бұрын

The whole point of this video was to show us an effective way to find the LCD. The problem was to find the LCD, not to add the fractions. Until, for the first time in my life, I learned about factor trees, I would have multiplied the denominators and simplified the end result. With large denominators, that can be very cumbersome. Using the factor tree method, for me at least, gave me one more small mathematical building block that I never learned 50+ years ago in school. I thought this was a brilliant video.

@ryanburnham1932 Жыл бұрын

@@tonywright560 with large denominators this too would be cumbersome. I was only in Highschool 20 years ago but I still remember teachers insisting we use the LCD to add/subtract fractions instead of just a common denominator. I do not remember learning about factor trees either, but my comment was more from the place of who cares about the LCD other than middle/high school teachers and what is there point. It would take less time and space to do two long multiplications than it would factor trees by hand, if we ignore the likelihood of a calculator in your pocket making the argument moot. And short of doing long division at the end, or having a calculator, any fraction with large denominators is likely to only give you a very vague idea of the answer in decimal form. I still see no reason to care about the LCD or seek it out for any real world applications, I work in the field of remote/off road system Alaska on-site construction office engineering/inspection, maybe there is some niche application where LCDs matter I just cannot think of one.

@tonywright560 Жыл бұрын

@@ryanburnham1932 Thanks for your reply, mate. I can think of one but your mileage might vary. The factor tree is something new that I learned in my dotage. For me, learning something new in maths helps make it fun. I don't disagree with you because I'm not an engineer and I don't have to use advanced maths in my profession. If you do and you have your way then I am not arguing. However, my father was an engineer, and for my first few years out of high school, before I forgot calculus, I could solve his thermodynamic problems for him. Not because I had any idea of the subject but just because he showed me the formula and I showed him how to solve it. He didn't have the benefit of the great things I learned from a great maths teacher. All the best.

@jjthekid1781 Жыл бұрын

Ryan you rather be fiction writer than be a math tutor

@gilbertopatino2616 Жыл бұрын

Thank you so much for another great video 🙏👍

@robertakerman3570 Жыл бұрын

Somehow I used arithmetic: #4 was common @ 1st. I'm glad He teaches "Math". A great foundation for future endeavors.

@witernpachise5132 Жыл бұрын

Thank you

@thomassicard3733 Жыл бұрын

I did it a different way that took 5 simple steps. (In fact, two approaches took just 5 steps, neither of which were the exponent involved method.) Apples and oranges... still came out the same answer: 59/160

@josgalgebra3784 10 ай бұрын

Pick what you need from 2*2*5 and 2*2*2*2*2. The number you need is 2*2*2*2*2*5. This as a regular whole number is 160.

@Vipre- Жыл бұрын

Why overcomplicate it? 20 ends in 0 so any whole number multiple will also end in 0, the quickest way to make a number ending in 2 end in a 0 is multiply by 5. 5 times 32 is 160 so the LCD is 160. Maybe a more complicated problem would've been a better example.

@enriqueiii9209 Жыл бұрын

Agree

@stevegledhill1575 Жыл бұрын

Exactly!

@tamaramelendez6425 4 ай бұрын

Use the GCD-LCM formula to show that in order to add the fractions 3/14 and 6/15 we can do no better than taking a common denominator equal to 210. Nee to show work but I do not understand it. Please help

@garthmcgibbon4285 21 күн бұрын

Mr Mathman I need to go back to learning Boolean Algebra to solve this!

@meganhoyle-keenan1828 9 ай бұрын

This would be so much better and more helpful if you got to the point.

@richardhole8429 27 күн бұрын

I use tons of shortcuts. The new student needs to learn the technique that works all the time before learning to spot the special case shortcut. If teacher goes to the special case first the student gets hopelessly lost when that special case does not apply to the next problem. We must teach the basics!

@duggydugg3937 Жыл бұрын

i would change the first fraction to .3/2 by multiplying upper and lower by .1 then multiply numerator and denominator by 16 = 4.8/32 then you get 11.8/32 = approx .368

@dougnettleton5326 Ай бұрын

So you would just randomly answer another question?

@davidduncan1362 2 ай бұрын

3/20+7/32 is interesting to solve. I simply write the factors in this bow tie multiplication, then I leave the multiplication unsolved until I find another factor that commonly goes into all three of these products. Be careful that your common factor goes into all three products when there is addition or subtraction incolved. Otherwise this method will not work. My work would look like this: (32×3+7×20)/(20×32). I see that the common factor for all three products, shown here, is four. Both of the thirty-twos can become eights and the twenty at the top can become a five. Do NOT touch the twenty on the bottom because that is part of the product of 20×32. After dividing these numbers by four, we should have this: (8×3+7×5)/(20×8). At this point, we can start solving the multiplication: (24+35)/160. The final step is to clean up this addition to get 59/160. Note that 59 is a prime number, so this is the best I can do at getting this fraction down to its lowest numbers.

@karenlight-crandell8951 Жыл бұрын

If I don't know it just by looking at it...I will go up the scale of multiples for the larger of the two denominators until I find a number that is also a multiple of the lower of the two denominator...which in this case is 160

@remediosdeleon3796 2 күн бұрын

It is very good H❤❤

@hayaat. Жыл бұрын

good

@user-wq8hp1bj4l 11 күн бұрын

This is like asking what time it is and he first has to tell you how the watch was made.

@Saibatou Жыл бұрын

160

@williamlynch1929 4 күн бұрын

160!

@cali-7617 Ай бұрын

Ultimate yapatron

@josgalgebra3784 10 ай бұрын

The example should take two minutes or less.

@harrymatabal8448 8 ай бұрын

Get me up when you have finished

@robertbridgen2950 2 ай бұрын

Easy way to get LCD is 20x32= 640 divide x 4 = 160 now 3x 32 and 20x 7 + together = 236 divide x4 = 59 so the answer is 59 over 160 because both can divide by 4

@trailerpark948 4 ай бұрын

lcd is 160 from guesswork. your explanation I never knew. so 160/20 =8 x 3 =24. 160/32=5x7 =35. so 24+35=59/160?

@uni-byte Ай бұрын

59/160

@billthorburn7476 10 ай бұрын

160 😊

@carlam6669 Жыл бұрын

The sword fight from Raiders of the Lost Ark comes to mind where Indiana Jones pulls out his gun and shoots the sword wielding attacker. If this problem occurred in real life I would divide the fractions out on my calculator and add the result to get (with rounding errors) an answer that has much more precision than is required given the accuracy of whatever it is I am measuring.

@amjPeace Жыл бұрын

I don't know why there is always so much emphasis on finding the very lowest common denominator. As long as both denominators can divide evenly into a number you can still proceed. For example, instead of using the factoring method I just quickly figured out that both 20 and 32 can divide evenly into 320. I should now be able to proceed to figure out the numerator values and then add. Of course I will then have to reduce the answer to lowest terms if that is required. As things stand now in school, most teachers would take points off on a test because the student didn't find the LCD, even though he/she demonstrated the ability to solve the problem.

@rodfulford4306 Жыл бұрын

The question was find the LCD! I wondered why he didnt finish the problem, then i realised....Always read the question thoroughly first

@clifforddeschaine6346 10 ай бұрын

I had it and changed my answer!!🤐

@francisdelpuech6415 9 ай бұрын

I’ve always used LCD so it’s an easy process to find that 32 has only 2 as multiple when 20 has 2 and 5 than you take the greatest power of each and voila

@TrevorSachko Жыл бұрын

Could you think of a more difficult way?

@pgbrandon 2 ай бұрын

Prime factors of 20 are 2*2*5 Prime factors of 32 are 2*2*2*2*2. What is common between them 2*2. What is uncommon 5*2*2*2. Together we have 2*2*5*2*2*2, or 160.

@Aereaux 8 ай бұрын

This is another easy LCD find. First the LCD has to end in "zero" because one denomenator is 20, and they only way to turn a 2 into zero is to multiply by 5. So the LCD is 160.

@Astrobrant2 5 ай бұрын

From 6:51 to 11:36 (4 minutes and 45 seconds) you went through a lot of steps, loading lots of stuff to remember and understand onto the student's brain, and lots of opportunities to make mistakes... when all you had to do was show how to extract the greatest common factor and multiply that by the two remaining factors. By the time you got to 6:58 (9 seconds) you were one step away from the LCD. 4x5 and 4x8 (shown) Extract the GCF (4) and multiply by 8 and 5. That's 160. DONE!

@suemoore1965 10 ай бұрын

Almost 7 minutes in before you even get to the problem

@MrMousley 10 ай бұрын

This is probably completely the WRONG way to do it but ... The 'easiest' denominator to find is obviously (20x32) 640 and 20 and 32 are both even and can be halved so (10x16) 160 is a possible denominator as well .. so let's check 160/20 = 8 160/32 = 5 YES .. 160 is a denominator but if we half 10 and 16 we get (5x8) 40 .. which 32 doesn't go into .. so 160 is it. This only works with two even numbers of course.

@jamesdismukes133 8 ай бұрын

All of that to look and see that the LCD must end in 0 and the first 0 is 5 times 32 or 160. Takes about 3 seconds.

@RobertConnollyOATS 5 ай бұрын

Sorry for me this was a bit confusing as I just multiplied 32x20 to get 640 as the LCD and the 32x3 and 20x7 gave me 236/604 which reduced to 59/160 just seemed a simpler method. Not that yours wasn't correct but seemed a bit more complex. Again love your videos and hope this doesn't come across as critical, your far smarter then me that I am sure of.

@my9goesbang 2 ай бұрын

lol i got the same answer. i thought i was trippin

@sheetalshah811 5 ай бұрын

I am a third grader and just figured this out.

@Blt-rr2lm 16 күн бұрын

Why?

@leland4831 9 ай бұрын

This took 2 seconds. 20 will only go into numbers that end in 0 so 32 x ? ends in 0? 320.

@mikemassey7403 10 ай бұрын

160 LCD

@NeuroSpicyVlog 15 күн бұрын

Those who can do, those who can't spend half of their video telling everyone how good they are rather than actually showing anything useful!

@pokemon2002208 5 ай бұрын

The answer is 84/160. Then 21/40

@brunogallego7507 8 ай бұрын

bros a professional yapper

@timnell207 10 ай бұрын

Much quicker….does 640 work…yes. How about 320 then. Yes. How about 160 then. Yep. How about 80…. Nope

@pmw3839 9 ай бұрын

Great hack. Does it always work? If so, I am surprised they don’t teach it.

@sjk1217 10 ай бұрын

I got there a lot quicker my way 😏

@michellemorgan205 10 ай бұрын

the answer is 39/160

@rossprentice4975 8 ай бұрын

@Jono2905 10 ай бұрын

Am I missing something here? I just saw the 2 and in order to get a zero you have to multiply by 5, therefore 5 X 32 = 160 in 5 seconds. I admit I did not watch the whole video.

@user-tg2gm1ih9g 2 ай бұрын

adding fractions is much easier using the bowtie method ... no need to strain your brain finding the LCD