PA_M5_S2_T1
Adding Decimals Transcript
Adding decimals is very similar to adding whole numbers. We could, of
course, rewrite my decimals as 3 + 125/1000, and then add the second
decimal as 4 + 814/1000. I can add the whole numbers together, 7, and the
fractional components to get 939/1000, and then rewrite that as my
decimal, or I can treat it more like I do my whole numbers. I can write
3.125 with 4.814 lined up directly below it with the decimals in their
own column and proceed as I would for whole numbers.
5 + 4 is 9, 2 + 1 is
3, 1 + 8 is 9, and
bring down the decimal
in the same column. 3
+ 4 is 7, and you'll
notice that I get
exactly the same
result as I got here
but this was a little
bit more
straightforward. So
what we want to do to
add decimals is put
them into a column
addition, lining up
the decimal places vertically in their own column, and then proceed as we
would for whole numbers.
Let's look at this problem. Jean has $4.35 in her
purse. Jim has $5.62 in his wallet. If they pool
their money how much will they have? I'm going to
write the $4.35 on the top. I'm going to write Jim's
$5.62 on the bottom, making sure that my decimal
points line up in our own column right here, and
then I add 5 and 2 to get 7, 3 and 3 to get 9, and
bring down the decimal point in the same location, 4
+ 5 is 9, so that their combined resources will be $9.97.
Now certainly we might have a lot of occasions where we add more than two
decimals at a time. I want to use the same column addition method here
that I did before.
I'm going to write my 12.2,
8.352, and 22.44. I want to
line up everything based on
this decimal in this column. I
will fill in with trailing
zeros on the right for any
decimal values that are missing
from my numbers because
trailing zeros don't change my
value.
And then I'm simply going to proceed as we always did. 0 + 2 + 0 is 2, 0
+ 5 + 4 is 9, 2 + 3 is 5, plus 4 is 9, and bring down my decimal, 2 + 8
is 10, plus 2 is 12, so I bring down the 2 and carry my 1. 1 + 1 is 2,
plus 2 is 4, so that my total is 42.992.
The key is line up the decimals then use the standard column addition
method we used with whole numbers.