The range of salaries for workers in the company is from $15,000 to $55,000 per year. Therefore, the total range of the salaries is $40,000 ($55,000 - $15,000). To find the probability that a randomly chosen worker earns an annual salary between $40,000 and $45,000, we need to find the proportion of the total range that falls within this salary range.
The width of the salary range between $40,000 and $45,000 is $5,000. So, the proportion of the total range that falls within this salary range is $5,000/$40,000, which simplifies to 1/8. Therefore, the probability that a randomly chosen worker earns an annual salary between $40,000 and $45,000 is 1/8 or 0.125, which is equivalent to 12.5%.