What is the average consumption of rice (in million kg) over the years…

Concept

The arithmetic mean of n quantities is their sum divided by n. When the quantity that has to be averaged is not printed in the table, it must first be constructed for every period from the definition supplied with the data, and only then summed and divided. The mean is also linear, so the mean of a difference of two series equals the difference of their means.

Applying it here

The quantity to be averaged is the annual consumption, which the table supplies only through the given relation consumption = production − exports. The per capita consumption column is not used, because it also depends on the population, and the population is not given.

Yearly consumption worked out from the table:

1. Add the five yearly consumption figures: 72.5 + 88 + 108 + 105 + 127 = 500.5 million kg.

2. Divide this five-year total by the number of years: 500.5 ÷ 5 = 100.1 million kg.

Cross-check and contrast

Because the mean is linear, the column means give the same result: mean production = 1062.5 ÷ 5 = 212.5 million kg, mean exports = 562 ÷ 5 = 112.4 million kg, and 212.5 − 112.4 = 100.1 million kg. Two slips are common on this pattern: averaging the production column on its own, which gives 212.5 million kg and leaves exports out altogether, and quoting a single year's consumption, such as the 2014 figure of 108 million kg, as though one year could stand for the five-year mean.

Average consumption of rice over 2012-2016 = 100.1 million kg.