Estimation and rounding

Estimation:
To replace all the digits of the number with zeros except for the largest place value digit>

Example:

325864 ==> 300000

12345789652 ==> 10000000000

Rounding:
To replace a number with a simpler close number
you can round up if the digit next door is 5 or more ,
and round down if the digit next door is 4 or less
Examples:
round the next number === > to the nearest

2315 to the nearest ten ==> 2320

51234 to the nearest hundred ==> 51200