In order to round off to the nearest hundred we have to check the place value on immediate right of the hundred place value. The digit on the right of the hundred is the tens digit. 47 can be written as 047.
The digit on the tens place is 4. So we have to round based on the value of 4.
The rule is if the number on right is 5 or greater than 5, the next digit would be rounded of the next higher digit and the digits on right will be replaced by zeros. If the number is less than 5, the digit will not be changed and all the digits on the right will be replaced by zeros.
In 047, 4 is less than 5. So the first 0 will not change, and the digits on right i.e. 4 and 7 will be replaced by zeros.
So 47 rounded off to the nearest hundred will be 000.