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From a grade 3 student...

Doubles

0+0=0
1+1=2
2+2=4
3+3=6
4+4=8
they all equal an even number
doubles help you because if you are in a situation like 1+2, you always look back at 1+1 or 2+2
doubles go from 0+0 to 10+10

Rounding Numbers
when you round a number, you always make a friendly number.
1-4 goes down, 5-9 goes up.
When you make a friendly number, you round to a ten.
You can round to any number that is in the tens column.

Adding
27+35=
1
27
+35
= 62

When you add a number, if the one's column adds more than 9, you put the 1 on top of the next number, and you leave the other number where it is.

Division
When you divide, the first number is how many things, and the second number is how many people.
For example,5 divided by 2 means there are 5 things and 2 people, that equals 2 remainder 1.
Or 5 divided by 2 means that each person gets 2 and a half.
So then 5 divided 2 equals 2.5

...from GG, March 12, 2013
Division
division is just like multiplication. For example, if 4x3= 12, than 12 / 3= 4.
Division is multiplication backwards.
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