Answer:
I believe Jayden will have done 1,073,741,824 sit-ups after 30 days.
Step-by-step explanation:
Each day of the month Jayden does double the amount of sit-ups as before. The days would add to be 2, 4, 8, 16, 32, 64.... 134,217,728 for the 27th day, 268,435,456 for the 28th, and then skipping to the 30th day you would get a total of 1,073,741,824 sit-ups.