
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
Dave and Doug need a total of 20 windows. If a promotion where two free windows are given for each batch of ten windows is used, Dave and Doug will get two free windows for the 20th window they purchase. Calculate their actual cost if they purchase the windows together.

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