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Current time:0:00Total duration:6:05

CCSS.Math:

- [Instructor] Last video, we
got a little bit of practice adding decimals that involved tenths. Now let's do slightly
more complicated examples. So let's say we wanna add four to 5.7, or we could read the second
number as five and 7/10. Pause this video, and
see if you can do this. The way that my brain
tries to tackle this is, I try to separate the whole
numbers from the tenths, so you can view this
as being the same thing as four plus five plus 7/10. All I did here is I broke
up the five and 7/10 into five plus 7/10, and the
reason why my brain likes to do that is because I can
then say okay four plus five, that's just going to be equal to nine, and then I just have to add the 7/10. So it's gonna be nine and
7/10 which I can rewrite, this is going to be
equal to nine and 7/10. Nine and 7/10 I could write as 9.7. Even though in future videos
we're going to learn other ways of adding decimals, especially larger, more complicated decimals, this is still how my brain adds four plus 5.7. Especially if I need to do it in my head. I say okay, four plus five
is nine, and then I have that 7/10, so it's going
to be nine and 7/10 or 9.7. Now let's do another example where both numbers involve a decimal. Let's say I want to add 6.3 to 7.4. So 6.3 plus 7.4. Once again, pause this video and try to work through it on your own. Well my brain does it the same way. I break up the whole
numbers and the decimals. Once again, there's many
different ways of adding decimals, but this is just one
way that seems to work. Especially for decimals like this. So we could view this as six and 3/10, so I'm breaking up the
6.3, the six and 3/10, into six plus 3/10 plus seven and 4/10. Seven plus 4/10, and then
this you can view as, so you could view this as six
plus seven, six plus seven, plus, plus 3/10, plus 3/10 plus 4/10, plus 4/10. If you add the ones here, you
have six ones and seven ones, that's going to be equal to
13, and then 3/10 and 4/10. If you have three of something
and then you add four of that, that's going to be 7/10, and we would write 7/10 as 0.7. Seven in the tenths place. Then what's 13 plus 7/10? Well that is going to be 13. This is going to be equal to 13.7. 13.7, and we are done. Let me do one more example
that will get a little bit, a little bit more involved. So let me delete all of these. Let's say I wanted to add 6.3 to, and I'm gonna add that to 2 point, 2.9. Pause the video and see if
you can figure this out. Let's do the same thing. This is going to be six
and 3/10, so six plus 3/10, plus two, plus 9/10, or you could view this as six plus two, so I'll put all my ones together. Six plus two, and then I'll
put my tenths together, plus 3/10, plus 3/10. Plus 9/10, plus 9/10. And so the six plus two
is pretty straightforward. That is going to be equal to eight. Now what's 3/10 plus 9/10? This is gonna get a
little bit interesting. 3/10 plus 9/10, and I could write it out. I could say this is three
tenths, this is nine tenths. Well 3/10 plus 9/10 is equal to 12/10. This is going to be 12/10, but how do we write 12/10 as a number? Well 12/10 is the same
thing as 10/10 plus 2/10. The reason why I broke it up
this way is 10/10 is one whole, so this is going to be equal to one. When you add these two
together, it's 12/10 which is the same thing as one and 2/10. So one plus 2/10 or, well let
me just write it that way. This I can rewrite as plus one plus 2/10, and then I think you
see where this is going. I could add the eight and the
one, and I get nine and 2/10. So nine and 2/10. So it's going to be 9.2. The reason why this one was a
little bit more interesting is I added the ones, I got
six plus two is eight, but then when I added the tenths, I got something that
was more than a whole. I got 12/10 which is one and 2/10, and so I added one more whole
to the eight to get nine, and then I had those 2/10 leftover. This is really good to understand because in the future when
you're adding decimals, you'll be doing stuff like
carrying from one place to another, and this is
essentially what we did. When we added the 3/10 plus
the 9/10, we got 12/10, and so we added an extra whole, and then we had the leftover 2/10. Hopefully, that makes some sense.