Estimating and Mental Math

From today's lesson if you need to remember ... :)

Estimating

When estimating round to the nearest large whole number you can handle mentally quickly.  If that is hundreds go to that number nearest 10's go there 50's go there. But you want to be as close as possible to the actual answer.

Remember if you see the word ABOUT it means to estimate.

Eg 95+52 you could do 100 +50 no need to go to 100 for the 50.

Friendly Numbers:

Mentally adding: One thing you can do is make a friendly number 137+298 make 298 into 300 and 137 into 135. You will get the same answer but easier numbers to add.
135
+300

No Extras

223+ 264

Recognize no number will carry then add down the line.

Compensation

For 2180+6432 you can move the numbers around to make ones that are easier to add in your head. But keep in mind if you do it to one number then you have to do the opposite to the other.

Eg 2180+20=2200

And 6432-20=6412

It is then a lot easier to add 2200 and 6412 down the line.

Counting on

For 2625 + 432 you can count on. Start with the Ones column 5+2=7 then the Tens. 3+2 =5 then the Hundreds 4+6 =10 take you extra and add it to the thousands. 2+1 =3 and you get 3057.