how to decrease one cells number while increasing another cells number

hello i have been working on 2 sheets receiving and selling item and QTY, or in other words i have a Stock IN sheet and a Stock Out sheet

is there some sort of a formula which links 2 cells, columns, together in a way that, if one cell's number increased the other would decrease automatically ?

say iv set 50 in cell a1, i want to set 10 elsewhere and the 50 in cell a1 will automatically decrease from to 40

here's my excel worksheets i uploaded it, plz it would be great help if someone provided me with Inventory manager.xlsx

oh im sorry about the A1 i mean to explain i was trying to explain i have nothing at A1 in my workbook sorry about that.

ok i explain my problem,i want the cells "9 E" in receive tab, all the numbers there to automatically subtract themselves whenever i write desired numbers in "9 E" Stock Out tab.

to clerify a bit, lets say we have the number 15 written in cell A1, and 5 written in cell A2, i want cell A1 to automatically be subtracted by the number which is written in A2, that means A1 will be 10

im sorry for the explanation seems like im having a hard time explaining ugh =l

oh im sorry about the A1 i mean to explain i was trying to explain i have nothing at A1 in my workbook sorry about that.

ok i explain my problem,i want the cells "9 E" in receive tab, all the numbers there to automatically subtract themselves whenever i write desired numbers in "9 E" Stock Out tab.

to clerify a bit, lets say we have the number 15 written in cell A1, and 5 written in cell A2, i want cell A1 to automatically be subtracted by the number which is written in A2, that means A1 will be 10

im sorry for the explanation seems like im having a hard time explaining ugh =l

i think i may be looking for a macro i want the operation which u just mentioned, like if i increase 1 cell the other cell automatically decreases, however i want this only with 2 cells, and yes the number has to be periodically changed, thats where im hitting the wall, however i thank you for ur help.

ok then, will do, and once again thx for looking up my thread i really appreciate u coming here and trying to help me out.