Consider the following sequence of events:
1. Start with a full gasoline tank.
2. Use half the gas.
3. Re-fill the tank with gasoline until it's full.
4. Use a quarter of the gas.
5. Re-fill the tank with gasoline until it's full.
What percentage of the gas in the tank after step (5) was originally there in step (1)?
Note: Assume perfect mixing between steps. Enter your answer as a percentage. For example, 58.4% would be entered as 58.4.