Estimating 3 by 2 digit numbers
I can estimate and multiply two digit whole numbers using the traditional algorithm.
Adding and subtracting decimals!
To add and subtract decimals , you need to line up the two decimals and just add. That's the same in Subtraction. Here's some example problems;
The Traditional Method!
The Traditional method is simple but it can be confusing. Let's learn it to check our work!
Open Number Sentences!
Open number sentences are just like normal number sentences, but you include a variable. YOu write an open number sentence BEFORE you do your work, so that it can help you think. The variable is the answer you need to find out. THe part you solve first, is the part you put in parenthesis. In this case, the open number sentence would be;
Subtraction Number Problems!
had 55 cupcakes. She gaave 20 to her neighbors, 15 to her friends, and threw 13 away because they were expired. How many cupcakes did Annie have left? (to eat.)
My Unit 2 Learning Model!
Thank you!
The point of estimating is to make it easy enough for you to do it in your head, or mentally.
Let's take this problem;
123 * 17=W
1.first we need to estimate it.
2. Look at the number 123. We need to round 123 to the hundreds place, so it's easy to multiply.
1 2 3
hundreds
tens
ones
3. To round a number to the hundreds place, you need to look at the tens place. If the tens place is 5 and higher, you round the hundreds place up. In this case it would be 2.
But when your tens place is four and lower, it stays the same.
Judging the data, our number would be rounded to 100.
100 * 20 = 2,000
this is our estimate.
Now let's check our work!
what about seventeen? Use the same rule (4 and lower to the floor, 5 and higher to the sky.) for seventeen. ....
if you did your math right, you'd get 20. 100* 20= 2,000.
1
2
3
1
7
*
In Traditional , you take one digit, and multiply it by the other digits. Then you take the next digit, and do the same thing.
1. first, we need to look at the 7 . It needs to be multiplied by 1, 2 ,and 3. In traditional , you go from right to left.
2. 7* 3 = 21, and you need to carry the one.
(clockwise instructions)
1
2
3. Next, you have to do 7*2. This equals 14. But don't forget to add the 2! This way, your answer is 16. Kepp the six, carry the one.
6
1
8
4. After that, you multiply 7*1. Add the one, and the answer is 8.
you're done with the first row!
5. Add a zero under the one, because we're shifting place values. This time we start under the 6.
6. look at the green one. 3*1=3, so we write 3 under 6.
7. 2*1= 2, write it under 8. And 1*1=1, write THAT next to the 6 on the left.
3
0
2
1
+
1
9
0
1
2
8. Then add! You should get 2,091.
Addition Story problems!
Rachel had 125 pencils in her pencil collection. Steve gave her 17 more. She gave her friend Martha, 43 pencils. How many pencils does she have now?
1 2 5
+
1 7
2
1
4
1
hopefully you know how to add. But if you don't, follow these easy steps!
7 +5=12. Keep the one, and carry the two.
2+1=3+1=4, so no carrying there.
1 stays the same, and your answer is 142 pencils.
Open number sentences next!
(1 2 3 + 1 7) = S
S = 1 4 2 pencils
Then you would subtract 43 by 142 to find the difference. You should get 99.
4 3
9
9
1. TO do this problem, you have to add all the numbers up. Then you would subtract them by 55.
2. 5 + 3= 8, no carrying.
2 0
+
1 5
1 3
8
3. 2 + 1+1 = 4, and your answer is 48.
4
4. Then, subtract it by 55 to get 7!
5 5
4 8

7
15
4
0
5. If you're still confused on what you need to do for open number sentences, go back a slide.
6. The Open number sentence is 55 (20+15+13)=P
2 3 . 1
+
7 . 9 8
8
0
.
1
1
1
3
4 5 . 3
2 3 . 1
.
. 2
2

2
(clockwise directions)
Multiplying decimals!
If you need to multiply decimals, and you don't know how, it's pretty easy! Just multiply it like normal traditional, (take out the decimals,) and put them back in. Here's a explanitory example;
12.3 * 17.5=x
1
2
3
1
7
5
*
first, you multiply 7*5= 35, keep the 5 carry the two.
multiply 5 by 2, and get 10. Keep the 0, and carry the 1. Add the carried one from 15, you should get 2.
5
1
2
1
6
For the green, 5*1=5, +1= 6.
Do the same for all the others, and you should end up with
1
6
8
1 2 3
5
3
5
1
2
The Doomed decimal..
Putting the decimal in the right spot SEEMS hard, but once you get it, it's really easy.
1 2. 3
1 7 . 5
2 1 5 . 3 5
You put the decimal how many spaces over it is on both decimal numbers, and dd thos two spaces together. The sum is how many spaces you move!
1,
1
1 + 1 = 2
Where DO you put the decimal? ...
... correct! In the middle of the first 5 from the left, and the three!
Thank You for grading and watching my learning model!
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My Unit 2 Learning Model!
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