When you round off a number, always check the number that is located at the right side. WHen that number is 5-9, round up. But when it is 0-4, dont change the number.
164, round to the nearest tens.
The tens is 6 and at its right side is 4, so dont change the tens digit. The answer is 160.
But when you say 'round the nearest hundreds then the answer will be 200. Because 1 is in the hundreds place and beside it is 6 so round up.