5 Rounds:
20 Pull-Ups
30 Pushups
40 AbMat Sit-Ups
50 Air Squats
     Rest Exactly 3:00 Between Rounds

A couple modification options for total volume is to drop the rounds to three or change the rep scheme to 10-20-30-40.

Looking for this session to take no more than 40 minutes.

The first two movements tend to give athletes the most trouble. Choosing proper modifications on both the pull-ups and the push-ups will ensure the best stimulus for each athlete. Score is total time including rest. 

Zachary Hamilton