Final answer:
Yearly average is calculated by taking the sum of all figures and dividing by their count. Seasonal index and deseasonalizing data involve adjusting for seasonal fluctuations. Inflation rates can be calculated using index numbers, taking into account changes from a base year.
Step-by-step explanation:
To calculate a yearly average for a set of numbers, you would sum all the numbers and divide by the count of the numbers, which gives you the mean value for the year. To find a seasonal index, you compare each season's data to the yearly average to see the relative level of activity in that season. The average seasonal index can be calculated by taking each seasonal figure and dividing it by the yearly average, then averaging these ratios across all seasons.
When you want to deseasonalize data, you divide the original data by the seasonal index, effectively normalizing the seasons to remove seasonal effects. This helps when analyzing trends without the fluctuations caused by seasonality. To simplify the total quantity spent over a year, you use index numbers and select a base year to compare against other years.
For calculating inflation rates using index numbers, you take the index number for the year in question and subtract the index number for the base year, then divide by the base year index and multiply by 100 to get a percentage. If 2003 is the base year, for instance, you would calculate the index number for subsequent years to see the relative change in prices compared to 2003.