It's simple. The package directions are to make a stock solution. Extreme precision with this stuff is gross overkill, and 1L is close enough to 1 quart to not matter. If I recall correctly, my supply of HCA is measured in US gallons and quarts. Start with about 3L of water at the recommended temperature and mix ALL the powder into that. Top off with cold water to 4L. That's your stock solution. For use, take 1 part of stock solution and dilute it with an additional 4 parts water. That's your working strength solution. Use it once and discard. So if you want to make only 1L of working strength solution you need only enough powder to make 200ml of stock solution. Divide the net weight of the HCA package by 4 to get the weight of the chemistry needed for 1L of stock solution, that is 500/4=125 grams. Now for 1L of working solution you only need 1/5 of that amount since the usual dilution is 1+4 for a total of 5 parts. Now do 125/5=25 grams. That's how much powder you need to make 1L of HCA working solution. This is basic arithmetic and you should know how to work the numbers. If you don't, go complain to your local school board because they've failed you.
The stock solution will last 3 months in a completely full and tightly stoppered bottle. Displacing the air with an inert gas in a partially full bottle qualifies as a completely full bottle.