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Adding decimals with ones, tenths and hundredths

CCSS.Math:

Video transcript

let's do some more involved examples using decimals so let's say we want to add four and twenty two hundredths to 61 and 37 hundredths like always I encourage you to pause the video and try to figure out on your own well the way that my brain tries to tackle it is it says all right I have four and twenty 261 and thirty seven hundredths how about I add the four plus the sixty one so it's going to be four plus sixty one and then separately let me add the twenty two hundredths to the 37 hundredths so then I'm going to add 22 hundredths plus 37 hundredths and so four plus sixty one is going to be equal to 65 and then 22 hundredths plus 37 hundredths well what's 22 plus 37 let's see 20 plus 30 is 50 and then 2 plus 7 is 9 and so it's going to be 59 hundredths so 59 hundredths this is going to be 65 and 59 hundredths which we can write as 65 and fifty nine hundredths now like I've mentioned in previous videos there's many different ways of adding decimals and in future videos we'll learn arguably faster ways of doing it but I want to show you multiple ways so you get a sense of at least ways to approach it and this is the way that I do it in my head if someone said hey something cost sixty one dollars thirty-seven cents and then you had to pay four dollars and twenty to two cents in tax how much did you have to pay in total this is how I would actually do it in my head I would get sixty five dollars and fifty nine cents let's do let's do another example so let's say that we have three and fifty three hundredths and we want to add that to 4 and seventy-two hundredths like always pause this video and see if you figure it out on your own so like we did in the previous example we could say all right we could add the ones three ones plus four ones so it's going to be three plus four and then we could add the hundreds and we could say plus fifty three hundredths plus fifty three hundredths plus seventy two hundredths plus seventy two hundredths now the three plus four is pretty straightforward that's just going to be the blue color this is just going to be equal to seven but what is 53 hundredths plus 72 hundredths well what's 52 what what's 53 plus 72 well three plus two right this way this is 53 hundreds hundreds and this is seventy-two hundredths well three plus two is going to be equal to 5 and then fifty plus seventy is equal to 120 so this is going to be 125 hundredths 125 hundredths so how do we write one hundred and twenty-five hundredths as a decimal or as just well this is a number well there's a couple of ways to think about it you could view this as 100 hundredths hundredths plus 25 hundredths plus 25 hundredths and the reason why I picked a hundred hundredths is because one hundred hundreds make a whole plus 25 hundredths and so 100 hundredths is just going to be one so there's going to be one plus 25 hundredths so I could write this 1 plus 0.25 and remember I'm adding that to the 7-year so it's going to be 7 plus the 1 plus the 25 hundredths so when we added the 53 hundred plus the seventy-two hundredths we get 125 hundredths which is the same thing as one and twenty-five hundred now the one we could add in the ones to the other ones and so this is going to be 7 plus 1 is equal to 8 8 and 25 hundredths so 8.25 now I'm going to introduce you a little bit to how people might tackle this more systematically and I want you to think about how this is the exact same thing that we just did so what you're going to see in the future is people are say ok line up the decimals so three point five three plus four point seven two the reason why people say line up the decimals is so that you're adding the right places to the right places for point seven two and then they say all right well let's go place by place and add it up which is essentially what we just did without doing it as as organized of a way here and I did it this way so that you really get the understanding of what's going on but you could say all right I have three hundredths plus two hundredths so I'm adding in the hundredths place so three hundreds plus two hundredths is five hundredths and then you could say okay then I have 50 hundredths plus 70 hundredths which I did over here or you could view this as five tenths plus seven tenths and five tenths and seven tenths is going to be equal to twelve tenths but you can't write 12 tenths in the tenths place but what you can do so you can't write so five plus seven is going to be twelve tenths but twelve tenths is the same thing as 1 & 2 tenths so you can write the two tenths in the tenths place and then you take the 1 and you put it in the ones place so five tenths plus seven tenths is one and two tenths and then you add the ones up and so you get one plus three plus four is eight so it's eight and two tenths and five hundredths or eight and 25 hundredths or 8.25 the exact same thing any way that you try to tackle it but hopefully it makes sense what's actually going on you're adding 100 your ending 100 to 110 stew tenths ones two ones and when you say you add ten to ten and you get something that's larger than one well that part that that is a whole number you can put in the ones place and we'll get much much more practice with this in future videos