My gym was FREEZING cold so I started with the stair master, thinking I would only do a five minute warm up, but it felt good to sweat so I kept going up to 20 minutes; about 1400 steps. Choose whatever type of cardio you like. Walking, running, arc trainer/elliptical, bike, etc etc.
20 minutes of cardio
For abs, hold a medicine ball for as many reps as you can while maintaining good form. Drop ball when needed and finish reps.
Ab work: 40 sits ups
20 oblique twists
30 sit ups
20 oblique twists
20 sit ups
20 oblique twists
10 sit ups
20 oblique twists