My title would be off, so I'll try to explain it as clear as I can.
Say I bought StockX at the price of X apiece.
== DURING BUYING ==
Let X = 10 as Unit Price of StockX
gross = qty x unit price(X)
charges = 10% of gross
total = gross + charges
eg.
gross = 100 x 10 = 1000
charges = (1000*.10) = 100
total = 1000 + 100 = 1100
Meaning, in order for me to own 100 units of StockX, I would need to pay for 11 apiece.
== DURING SELLING ==
Let X = 13.45 as Unit Price of StockX
gross = qty x unit price(X)
charges = 10% of gross
total = gross - charges
eg.
gross = 100 x 13.45 = 1345
charges = (1345*.10) = 134.5
total = 1345 - 134.5 = 1210.5
total gain = (1210.5-1100) = 110.5
gain% = (110.5/1100)*100 = +10.04% (positive gain)
In this case, I have to wait for the price of StockX to settle at 13.45 apiece before selling if I wanted to have a gain of 10% for my investment.
So say, if I want to have a 20% gain, what should be the price of X? How can I translate this into a formula to identify X if I wanted to take action at a certain percentage.
Also, what do you call this kind of mathematical problems? (Is this probability)?