Difference using an unmarked number line for iPad

Find the difference between two numbers by counting on from the smaller number to the larger number. Children must add the fewest numbers possible, so are encouraged to develop more efficient mental methods. The addition is also shown as jumps on a number line.Levels include counting up to 10, 20, 50 or 100, finding the difference between 2-digit numbers, 3-digit numbers and decimals.