Phillips used 125, 130, 135, 140 and 145 as class centres. What class intervals did she use?
Or do u need to see the graph to solve this?
No, you don't need to see the graph to give the correct answer. You have supplied sufficient information to calculate the class intervals.
Class interval is the distance between classes. The distance can be calculated by taking the difference between class centres, class starts, or class ends.