A penny doubled each day for a month: day 1: $0.01 day 2: $0.02 day 3: $0.04 day 4: $0.08 day 5: $0.16 day 6: $0.32 day 7: $0.64 day 8: $1.28 day 9: $2.56 day 10: $5.12 day 11: $10.24 day 12: $20.48 ...