a. SCALE: Set the scale of the number line that is:
• Type in a number >=1 and <=500.
• Then click on the Set Scale button.
Remember: arrow for first number starts from 0, arrow for second number starts from end of first arrow.
• Now click on Ready for First Number.
b. FIRST NUMBER: Click and drag the point on the red slider to the value of the first number.
• Now click on Ready for Second Number.
c. Second Number: Click and drag the point on the blue slider to the value of the second number.
We are subtracting a negative number, so the arrow shifts direction twice, that is, the blue arrow moves to the right. Does this look like addition of a positive number?
d. OPERATION: What is the result?
• Click on "Show Result " to see it on the number line.
e. EQUATION: Write down the equation for the operation and then do the operation. Remember that subtracting a negative number is like adding a positive number.
• Click on Show Equation to check your answer.
Move the red slider to a positive number. (Notice the blue slider moves back so we don't go off the number line 
). Now we are adding 2 positive numbers" - easy! Move the red slider to a negative number and say with words how you calculate the result of adding a negative and positive number.
• Click on Reset to start over.