
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
Given a seven-digit phone number, with four known digits (6, 6, 1, 6, 8, 9, unknown), calculate the probability that the missing digit is exactly one of the remaining five options.

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