Rounding: closest to Teacher’s Notes

This exercise is for students to use independently of the teacher to practice number properties.

Number Framework domain and stage:

Grouping/place value, stage 5

Number, level 2

Numeracy Project book reference:

This activity does not follow on from an activity in the numeracy project books

Prior knowledge. Students should be able to:

• Identify when a number is “closer to”

During these activities, students will meet:

• Rounding to the nearest ten, hundred or thousand
• The sign that means “approximately equals”

Background

This activity is an introductory exercise designed to introduce students to the idea of approximate numbers and rounding. It is knowledge based.

Exercise 1
This exercise introduces students to talking about the approximate size of numbers. In doing this it also introduces them to a new symbol (≈ or the ‘squiggly equals’). Teachers need to be aware that this symbol needs to be used in the context of a problem, with the questions in this exercise being a very simple class of these. If taken out of the context of the problem, and the numbers in that problem, its use can lead to some nonsensical statements. For example, saying that 150 is approximately 200, or pi (3.1415928…) is close to zero is not very helpful mathematically. However in the context of the problem 47 ÷ 123,456,789 saying that 47 ≈ 0, so the answer is approximately zero does make sense

Questions 12 to 16 are deliberately vague. Working in the context of approximate numbers can be like this. For one problem it may be appropriate to say that 56 is close to 60. For another, it may be that saying 56 is closer to 100 is better. Discuss with students which numbers they say they were closer to, and why they made that choice.