
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
A company, aiming to accurately grasp the market and make good product plans, conducted a market survey on a product: the product was sold for 50 days, and it was found that the daily sales volume \(x\) was distributed within \([50,100]\), and the distribution frequency of sales volume \(x\) is \(f(x)= \begin{cases} \dfrac {n}{10}-0.5, & \text{for } 10n\leqslant x < 10(n+1), \text{ where } n \text{ is even} \\ \dfrac {n}{20}-a, & \text{for } 10n\leqslant x < 10(n+1), \text{ where } n \text{ is odd} \end{cases}\).
- (I) Find the value of \(a\).
- (II) If the sales volume is greater than or equal to 80, then the day is considered as a high-sales day, otherwise, it is considered as a low-sales day. According to whether it is a high-sales day, randomly select 5 days from these 50 days using stratified sampling method, and then randomly select 2 days from these 5 days. Calculate the probability that exactly one of these 2 days is a high-sales day (consider frequency as probability).

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