The first quartile (Q1) is the median of the lower half of the data set. In the context of car sales, if 19 out of 65 salespersons sell 4 cars, Q1 would be 4 cars, indicating that 25% of the salespersons sell less than or equal to 4 cars.
The first quartile (Q1) of average sales over 12 randomly selected days is the value below which 25% of the data falls. To determine Q1, you need to calculate the median of the lower half of the dataset (excluding the median if there is an odd number of data points). Since the median (Q2) is known to be the sale of 7 cars, Q1 would be the middle value in the ordered list of the lower half of the data.
For example, if you have a dataset of weekly car sales by 65 car salespersons with the values: 14 sales of 3 cars, 19 sales of 4 cars, 12 sales of 5 cars, 9 sales of 6 cars, and 11 sales of 7 cars, you must first order these from least to greatest and then take the middle value of the lower half to find Q1. In this case, since 19 salespersons sold 4 cars, and this is the largest number less than 7 (the Q2), the first quartile would be 4 cars.
the first quartile provides valuable insight into the distribution of data by indicating the value below which a quarter of the data lies. It's a measure of the spread of the lower portion of the dataset.