Four students were discussing how to find the unit rate for a proportional relationship. Which method is valid?

1. “Look at the graph of the relationship. Find the y-value of the point that corresponds to x = 1. That value is the unit rate.”

2. “Look at the graph of the relationship. Count the number of units up and the number of units to the right one must move to arrive at the next point on the graph. Write these two numbers as a fraction.”

3. “Look at the graph of the relationship. Find the x-value of the point that corresponds to y = 2. That value is the unit rate.”

4. “Look at the graph of the relationship. Find two points which have y-values that are one unit apart. The unit rate is the difference in the corresponding x-values.”