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decimal lesson
menu project
by
TweetLegolas is boss
on 31 May 2014Transcript of decimal lesson
step 1
Input 3
Even when you line up the decimals if
your number doesn't have the same
place value can get confusing but there is a
solution to that.
step 2
Now its your turn !
Next you have to line up the decimal
points. This is very important so you add the
right numbers, but how?
How to add and subtract decimals
First you want to estimate your answer so when you get your answer you know if your answer is reasonable. But how?
lets say your problem is
20. 6 + 31. 2. You want to
round it to the nearest whole
number so you look at the
number in the tenths place.
The first number is 20 .6. The
number in the tenths place is
6. 6 is more than 5 so you
round it up . Your new
number is 21. do the same with
your next number. 2 is in the
tenths place and that rounds
down so you just keep
31 the same but take the
decimal away. Then add the
estimates together to get your
. answer
20.6
6 >5
2<5
round up
round down
21
If your numbers
31.2
0
31
20
+
51
That is your estimation
lets say your numbers are 23
.
7 and
2
.
11.
the simple way to add them up is like this...
23.7
2.11
+
448
the answer is wrong since I did not line up the decimal points
We need to avoid confusion of place value so you need to line up the decimals to get the correct answer, here is what you do.
23
.
7 2
.
11
1.first you have to notice where the decimal place is on each number
Then you have to match up the decimals so one is on top of the other, like this.
23.7
2.11
the decimals are alined so now you can add and you get..
25.81
Ghost zeros
0
what are ghost 0's ? Ghost 0's are 0's that are just place holders with no value like this one.
21.3000000000
you could put any number of zeros at the end but if you put them before the end of the decimal it does change the value and its not a ghost 0. Here is a example.
21.03
not a ghost zero
But some times you can't tell if the 0 is a ghost or not if its at the end so you can draw the zero in different ways.
Now you know how to estimate your problem,
line it up, add ghost 0's to make it easier. Now you just have to add or subtract the problem. Let's try it.
Here is your problem it has already been estimated and lined up with a ghost zero so you can just subtract.

0
do you know how to add
51.3345 + 21.79
13
estimate
2 0.3 7 2
7 . 1 1 1 1
13.2609
Now you have to apply basic rules of subtraction all thats different is that you have to bring down the decimal.
Now that you practiced once lets go back to the problem at the start and we'll do all the steps we reveiwed to day
YES!!
51.3345
21.7 9
Estimate
Line it up
Bring in the ghost
0
Add it up
Your estimate was
73
(
Bring down the decimal)
Your problem should have looked like
21.79
51.3345
+
With ghost zeros it would have looked like
21. 79
51.3345
0 0
Your answer is
73.1245
decimals rock co.
being the correct answer
Thank you I hope you learned alot
1, 2 ,3, 4
5, 6, 7, 8, 9
31.
?
2.11
23.7
You would get
Hooray
Like this
0
0
0
0
do you know how to add
51.3345 + 21.79
You can do it
21.7 9 +
51.3345
You got this
21.7 9
51.3345
+
51.3345
21.7 9
+
Keep it up
Finish strong
Is your answer
By Bella
Full transcriptInput 3
Even when you line up the decimals if
your number doesn't have the same
place value can get confusing but there is a
solution to that.
step 2
Now its your turn !
Next you have to line up the decimal
points. This is very important so you add the
right numbers, but how?
How to add and subtract decimals
First you want to estimate your answer so when you get your answer you know if your answer is reasonable. But how?
lets say your problem is
20. 6 + 31. 2. You want to
round it to the nearest whole
number so you look at the
number in the tenths place.
The first number is 20 .6. The
number in the tenths place is
6. 6 is more than 5 so you
round it up . Your new
number is 21. do the same with
your next number. 2 is in the
tenths place and that rounds
down so you just keep
31 the same but take the
decimal away. Then add the
estimates together to get your
. answer
20.6
6 >5
2<5
round up
round down
21
If your numbers
31.2
0
31
20
+
51
That is your estimation
lets say your numbers are 23
.
7 and
2
.
11.
the simple way to add them up is like this...
23.7
2.11
+
448
the answer is wrong since I did not line up the decimal points
We need to avoid confusion of place value so you need to line up the decimals to get the correct answer, here is what you do.
23
.
7 2
.
11
1.first you have to notice where the decimal place is on each number
Then you have to match up the decimals so one is on top of the other, like this.
23.7
2.11
the decimals are alined so now you can add and you get..
25.81
Ghost zeros
0
what are ghost 0's ? Ghost 0's are 0's that are just place holders with no value like this one.
21.3000000000
you could put any number of zeros at the end but if you put them before the end of the decimal it does change the value and its not a ghost 0. Here is a example.
21.03
not a ghost zero
But some times you can't tell if the 0 is a ghost or not if its at the end so you can draw the zero in different ways.
Now you know how to estimate your problem,
line it up, add ghost 0's to make it easier. Now you just have to add or subtract the problem. Let's try it.
Here is your problem it has already been estimated and lined up with a ghost zero so you can just subtract.

0
do you know how to add
51.3345 + 21.79
13
estimate
2 0.3 7 2
7 . 1 1 1 1
13.2609
Now you have to apply basic rules of subtraction all thats different is that you have to bring down the decimal.
Now that you practiced once lets go back to the problem at the start and we'll do all the steps we reveiwed to day
YES!!
51.3345
21.7 9
Estimate
Line it up
Bring in the ghost
0
Add it up
Your estimate was
73
(
Bring down the decimal)
Your problem should have looked like
21.79
51.3345
+
With ghost zeros it would have looked like
21. 79
51.3345
0 0
Your answer is
73.1245
decimals rock co.
being the correct answer
Thank you I hope you learned alot
1, 2 ,3, 4
5, 6, 7, 8, 9
31.
?
2.11
23.7
You would get
Hooray
Like this
0
0
0
0
do you know how to add
51.3345 + 21.79
You can do it
21.7 9 +
51.3345
You got this
21.7 9
51.3345
+
51.3345
21.7 9
+
Keep it up
Finish strong
Is your answer
By Bella