# Surf for More Math

## Lesson 4 - Determining the Difference

Use these interactive activities to encourage students to have fun on the Web while learning about determining the difference. Students can try these activities on their own or in pairs.

### Goal

Use various strategies to determine the difference between two 2-digit numbers.

### Instructions for Use

Counter Square lets students solve subtraction problems using a 100 chart.

To use Counter Square, click the "Make Counters" button to create multi-coloured counters. Drag and drop them onto the grid to show number patterns. Click "Ideas" for suggestions on how to use counters on the grid.

Interactive Calculator allows students to subtract 2-digit numbers and display them on a 100 chart.

To use Interactive Calculator, start by clicking a 2-digit number on the interactive calculator. This number will appear in the calculator window. Click the "-"button on the calculator, and then click a different 2-digit number. Click the "=" button on the calculator.