How do companies convince people that supplements work? to what extent do they work?

Companies usually use strategies such as testimonies, and others such as overgeneralization (over-simplification) where they say a very broad claim that may not be completely true. Or, it may specifically leave out certain details in order to convince you.

 Required reserve=$36  million

Explanation:

In a fractional banking system, banks are required to maintain  a proportion of  their total deposit for precautionary reasons by banking authority.

The proportion is known as the required reserve ratio and is always given as a percentage of the total deposit.

The required reserve = required reserve (%) × Total deposit

                                  = 12%× 300 million

                                   =36  million

 Required reserve=$36  million