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Current time:0:00Total duration:6:26

CCSS.Math:

in this video we're going to introduce ourselves to the idea of adding decimals and I encourage you as we work through these problems to keep pausing the video and seeing if you can think about it on your own before we work through it together and we're going to build up slowly and in future videos we're going to find out faster ways of doing it but the way we're learning it in this video in the next view is to really make sure we understand what is happening so let's say we wanted to add zero point one two zero point eight or you could say we're adding one tenth to eight tenths pause this video and see if you can figure that out well there's a couple of ways to think about it you could say hey look zero point one that is 1/10 and zero point eight that is eight tenths and so if I have one of something and I add eight more of that something so if one tenth and I'm going to add eight more tents well I'm going to end up with nine of that something in this case we're talking about tenths so that is going to be equal to nine tenths that's one way to think about it another way we could think about it visually so let's say we take a whole and we were divided into tenths which we have right over here so if we say this whole square as a whole we divided into ten equal sections so each of these white bars you can view as a tenth so we have one tenth so let me fill that in so one tenth whoops that's not what I wanted to do we have one tenth right over there and to that we want to add eight tenths so one two three four five six seven eight and so how many total tenths do I now have well let's just count them up we have this one here one two three four five six seven eight nine these are really saying the same thing all of this together is going to be a little neater all of this together is going to be nine tenths now in either case how do we write nine tenths in decimal form well we go to the tenth place which is one space on the right side of the decimal we say hey we have 9/10 this is the tenth space right over here so that's just saying we have nine tenths we have nine we have nine of these tenths right over here so let's keep building let's try to do let's do another example so let's say that we let me clear all of this out so let's say that we want to add do these with different colors so let's say we want to add I have trouble it's my pen isn't working let's see let's say we want to add my pen is oh here we go let's say we want to add three tenths and to that we want to add nine tenths what is that going to be well you could do use the same idea if you say this is three tenths and this is 9/10 plus nine tenths well that's three of something and if I add nine of them well that's going to be 12 3 plus 9 is 12 so we could say this is going to be equal to 12 tenths now this one might be a little bit counterintuitive twelve tenths what does that mean well one way to think about it this is 10 10 10 10 plus 2/10 and what are 10 tenths well if I have ten tenths this right over here is one whole so that is going to be 1 so we have 1 & 2 tenths so how do we write 1 & 2 tenths well we could write it as in the ones place we just write a one and then then in the tenths place we write our two tenths so it's you could say it's equal to 1.2 or you could say it's equal to 1 & 2 tenths which is the same thing as 12 tenths now if we want to see that visually let's get our diagram out again so actually I'm going to make put two of these here so one and then a second one and we want to add so let's start with the 3/10 so let me color these in really fast so use that light blue color so that is 1/10 this is 2/10 its coloring them in really fast and this is 3/10 and then to that we're going to add nine tenths so to that we're going to add one two three I'm not coloring them in fully four you get the idea five almost there six and you're color faster seven seven eight nine so there you have it I have added nine tenths you notice I've colored in nine I've colored in yellow nine of the tents and before I had three of the tenths colored in and when you add them all together what happens well the three tenths plus the seven tenths right over here they made a hole so this right over here is our one and then we also have another two tenths left over and so this is where this is our 0.2 or two tenths so it's going to be one plus two tenths which is one point two so hopefully this gives you a good sense of how we think about adding decimals and even though in the future we're going to figure out faster ways of doing it or miss more systematic ways of doing it this is still the way that that I still do it in my head if someone walks up to me on the street and says hey add 0.3 to 0.9 that's how I think about it