Purpose

The purpose is to develop useful strategies for mental calculation when counting in 10s and 100s.

Achievement Objectives

NA2-2: Know forward and backward counting sequences with whole numbers to at least 1000.

Specific Learning Outcomes

state the difference between numbers by counting in 10s and 100s

Required Resource Materials

A number line marked in 10s to 100, to 200 to 300 etc

A number line marked in 100s to 1000.

Activity

- Write 20 and 70 on the board. (vary the starting point to include numbers beyond 100 – as confidence grows then include numbers bridging the decades)
- Students take turns counting, verifying each others counting.
*When you count from 20 – 70 how many times did you add 10?*

What is the total of 5 tens?

How much more than 20 is 70? - Write 200 and 700 on the board. (Vary the starting point.)
- Students take turns counting, verifying each others counting.
*When you count from 200 – 700 how many times did you add 100?*

What is the total of 5 one hundreds?

How much more than 200 is 700? - Write 220 and 270 on the board. (Vary the starting point)
- Students take turns counting, verifying each others counting.
*When you count from 220 – 720 how many times did you add 100?*

What is the total of 5 one hundreds?

How much more than 220 is 720?