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Current time:0:00Total duration:3:25

Roman numerals worked example

Video transcript

so let's solve a couple of questions to see if we really understand this well so I'm gonna take 79 first and I and I want you to stop and solve this on your own and see what answer you get and how you thought about it and see if the both of us are thinking similarly so when I look at 79 in my brain I'm going okay 79 is bigger than one bigger than five bigger than 10 bigger than 50 but not bigger than hundred so I'll definitely need a 50 to denote this number in the Roman numeral so I'll write in L so now I know represented this 79 is 50 plus maybe I should write the plus here plus some 29 and I can forget about this 50 because of already written as is for it now I need to represent this 29 so what am i doing I can I can forget that I started with 79 and all that now I all have to care about is 29 and whatever I get added to this so I look at 29 do the same thing bigger than one bigger than five bigger than ten but less than 50 so it's between 10 and 50 how many tens are there there are two tens so I'm gonna write X X and now I know I've brought this down to this 29 I've written it as 20 plus nine and I can forget about this 20 now I have nine now to look at 9 and ask myself how do I write nine and I don't have to care what came before that all I need to care about is how do I write nine and I know how to write nine minus IX that's how I write it so I'm gonna write 9 as I X and I'm showing this separately so you can see that this alone is written in the subtractive notation so how do you read this number you'll go 50 plus 20 at 70 plus when you come here it'll be like oh this is not 21 but if this number had only been this much you'd I said that's 50 plus 20 plus 171 but then when I add this here then you can see it's one less than ten that's nine so seventy-nine and I hope you this is the same thought process that you used as well or maybe a better one this 49 is very interesting I mean I was tempted when I saw 49 my temptation was to write I L like why not one less than 50 it turns out that we do not do this like like we said we only use subtractive notation for these numbers for 949 T or 400 900 so how do I think about this number I can look at this number and go okay this is less than 50 greater than 10 and it has four tens in it what is 40 and this is where it can get a little tricky at first what is 40 I want I don't have to write 40 as Excel so right xl4 40 and then I know that I've written this number as 40 plus 9 and I've already shown what this 40s now let's give a different color for nine now how do we we don't we can forget about this 40 that's what is Excel over here what is nine I already know how to write nine that's IX so I write I x over here so x l IX will be 49