The activity-selection problem

Q1. Not just any greedy approach to the activity-selection problem produces a maximum-size set of mutually compatible activities. Give an example to show that the approach of selecting activity of least duration from those that are compatible with previously selected does not work. Do the same for the approaches of always selecting the compatible activity that overlaps the fewest other remaining activities and always selecting the compatible remaining activity with the earliest start time.
Q2. Write a method to count number of nodes in B-Tree that has no children
Q3. Write a method to count the number of nodes in B-Tree
Q4. Write a method to find the largest value in B-Tree