what are the factors that determine the demand of fast moving consumer goods like washing machine detergent?

Answer 1

you can't lump fast moving consumer goods together...
for example: food and detergent has different factors

demand on a particular type of product will appear if the supporting factors are fulfilled

ex: to calculate demand for washing machine detergent in an area, you need to calculate how widely washing machines are used, number of washing machines / laundromats in an area, local clothing habits (not all clothing are machine washable), population

demands will increase along with growth of the factors mentioned above

Answer 2

Price, qulaity, distribution channels, brand equity....

pretty much the same as most consumables.