Primary Four: Round to Nearest Tens or Hundreds

In Primary Four Mathematics Syllabus (2007), students need to learn how to round off numbers to the nearest ten/hundreds. In this case, the schools are teaching students to

1) draw a number line
2) write two nearest tens/hundreds where the number lies in between.
3) Find out which nearest ten/hundred is the number closest to, then choose it as the answer.

The common confusion comes in getting the two nearest ten, especially if they have the digit '9' in the tens or hundreds place. Students usually will be confused on how to get the higher nearest ten/hundred.

What parents can do is to teach them this method.

1) Write the lower ten/hundred where the number will fall above. If it is a 5 digit number, take the first four digits (for rounding to the nearest ten) or the first three digits (for rounding to the nearest hundred). After taking the first four digits, add another zero behind (for rounding to the nearest ten) to get the lower ten. Or for rounding to the nearest hundred, add another two zeroes to the first three digits to get the lower hundred.
2) Add ten/hundred to the lower number that is derived in Step 1 to get the higher ten/hundred. In this case, there will be less confusion as to which number is chosen.
3) Looking at the digit in the ones place, for rounding to the nearest ten or looking at the digit in the tens place, for rounding to the nearest hundred. If the digit is 1,2,3,4 then take the lower ten/hundred. If the digit is 5,6,7,8,9 then take the higher ten/hundred.

Now some parents might be thinking why not ask the student to immediately look at the digit after Step1 to get the answer, but my opinion is that it would be better to teach students the more complete and easier to master method, which is teaching all the three steps.

The common mistakes that students might make while carrying out the recommended three steps are during the addition, students make careless mistakes, thus it is recommended that parents encourage students to check their answer after completing Step 2 to make sure that the addition is done correctly.