3 rounds for time of:
25 dumbbell push jerks
50 double-unders
25 weighted step-ups
50 double-unders

Men: 50-lb. dumbbells, 24-in. box
Women: 35-lb. dumbbells, 20-in. box

Tips: Reduce the weight and reps in order to move continuously with very few breaks. If you struggle with double-unders, reduce the reps to something you can complete in 3-4 sets or modify to single-unders.

http://www.endofthreefitness.com/a-ridiculously-awesome-yet-brief-guide-to-double-unders/