Rest as needed, break up in 50/25/10s if needed (i.e 10 squats, 10 second wall sit, 10 lunges and go through 10 times to get to 100)! If listed as 100 second exercise, simply time yourself for 100 seconds (1 minute and 40 seconds). Push yourself and don't quit!!
100 squats
100 second wall sit
100 lunges
100 second push ups
100 bicycle crunches
100 second plank
100 reverse crunches
100 seconds burpees
100 squat jacks
100 second scissors