Rounding & Estimating

Rounding: 
When it comes to rounding, it's really simple. If you were asked to round, go by these rules. 
1) If it's 5 and higher: round UP
2) If it's any number lower than 5: round down. 
For example, I chose the number 126. In this case, we're rounding it up to the nearest ten. Since it ends in a "6", we would have to go up. The number would now be 130.
If the number was 124, we would round it to 120 since 4 is lower than 5.

Estimating:
In some or most cases, estimating has to do with rounding. To estimate is to take a smart guess, but there has to be a reason.
For example:
- Adding: 126+163
     I could round 126 to 130 and I could round 163 to 160. So now the two numbers are 130 and 160.
     130+160= 190. 
     Now if you calculate the actual number, it would be 289. 

-Subtracting: 352-221
    I could round 352 to 350 and 222 to 220.
    350-220= 130
    Now if you calculate the actual number, it would be 131. 

In some cases, the two answers could be pretty close.