# Big steps

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
1. 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)
2. 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?
3. Write 200 and 700 on the board.  (Vary the starting point.)
4. 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?
5. Write 220 and 270 on the board. (Vary the starting point)
6. 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?