
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
At an oil refinery, a tank was filled with crude oil containing 1.5% sulfur. A portion of this oil was sent for production, and an equal amount of oil containing 0.5% sulfur was added to the tank. Then, the same amount of oil as before was sent for production again, but this time oil containing 2% sulfur was added. As a result, the sulfur concentration in the oil in the tank returned to its initial value. Determine what fraction of the oil in the tank was sent for production twice.

Present the answer in LaTex format: \boxed{Your answer}
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