ROI formula

[cdpaul]

Hi,
I have a betting spreadsheet and would like to add a ROI (Return on investment) formula which I understand to be won/bet x 100. My "win" amounts are in colums c3 to c500 and my "bets" are in column b3 to b500. I cant seem to create the right formula to show as a % the ROI and in particular to show it as a minus where necessary.

Can anyone help please?

 

[JoeMo]

Adjust the ranges to suit.

Excel Workbook
	B	C	D	E	F	G	H
1	Bet	Won	Gain/Loss		Tot Inv	Net	ROI
2	100	200	100		900	-280	-31.1%
3	100		-100
4	100	150	50
5	100		-100
6	100	120	20
7	100		-100
8	100		-100
9	100	150	50
10	100		-100
Sheet3

 

[par60056]

Wouldn't ROI be (Won-Bet)/Bet? So if bet looses and won is 0, then you have -100%