Hi,
This is a typical market size question. You are given a question and have to guess all the numbers to arrive at the solution. This is how I would have approached it:
- Choose a metropolitan city and check if ok with the interviewer. Alternatively, choose a "standard" metropolitan city and you would have to guess how many people are there
- Guess the number of people that live in the city + tourists
- Assume the average life expectancy is 80 years
- Divide the population in 4 age groups and assume they are equally distributed (so that the amount of population per group is going to be the same and = total people/4)
- Define the sources of orange juice that could be sold in the metropolitan cities (e.g., big supermarkets, shops, petrol stations, temporary markets, ...)
- Assume that the average bottle of orange juice is 1 l (alternatively, you can also use two measures for the can 0,5 and bottle 1,5)
- Guess per every source and bottle size the percentage of people purchasing it per year (so for example if for you they are purchasing 2 times/year, double the percentage checking with the interviewer)
- Obtain the litres of orange juice sold per every "channel" and sum them up
