The correct answer is B. Index numbers.
An index number is a statistical measure of average change in a set of data over time. It is used to compare the value of a variable in different time periods or to compare the values of different variables in the same time period. Index numbers are often used to measure the purchasing power of money.
The purchasing power of money is the amount of goods and services that can be purchased with a given amount of money. It is affected by inflation, which is a general increase in prices over time. When prices increase, the purchasing power of money decreases. Index numbers can be used to track changes in the purchasing power of money over time.
The arithmetic average is the sum of a set of numbers divided by the number of numbers in the set. It is a simple measure of central tendency, but it can be misleading if the data is skewed.
The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals of a set of numbers. It is a less common measure of central tendency than the arithmetic average.
A time series is a sequence of data points that are ordered by time. Time series are often used to track changes in a variable over time.
In conclusion, the correct answer to the question “Which statistical measure helps in measuring the purchasing power of money?” is B. Index numbers.