I need to know the concept

The number "487" is a three digit number and we are to round it to the nearest hundred. First of all we need to know what does it mean by "rounding the number to the nearest hundred". It means quickly expressing the given number such that its last three digits ends in 100, 200, 300 and so on...But we have certain laws to do so. To round any number to its nearest hundred, we first quickly notice the digit in hundreth place, here it is
**4**. Now we certainly know that this digit is of interest that has to be either increased by one digit up or be unchanged. To decide whether or not to increase this digit depends on the digit right to it (i.e., the digit in tenth place), here it is **8**. If it is greater than **5**, increase the digit
**4** by one digit making it **5** and append two zeros after this digit. In case if it is less than
**5**, do not change the digit **4**, instead keep it same and append two zeros after this digit. Here
**8>5**, so increase **4** by one digit and make it** 5** and append two zeros after this to make it 500. Hence the rounded number of 487 to its nearest hundred is
* 500*.

Special case:

In case if the digit in tenth place is **5** (neither greater or less than the digit in hundredth place), we check the digit in unit place. If it is greater than
**0**, increase the digit **4** by one digit making it **
5** and append two zeros after this digit. In case if it is zero, do not change the digit
**4**, instead keep it same and append two zeros after this digit.