Maths Question

catfloppo's suggestion is a good one.
YOu can also download your betting profit and loss into a spreadsheet and calculate this very easily.

For a bit of fun, I tried to work it out using only the data you provided, it won't be completely accurate, as you can't tell the exact amount of commission generated purely from betfair points, but it will be extremely close. Using only the information of betfair points for the week and Net PnL, you can use the following formula:

a*.02+(a*.98-b)*.03=c


a = GP on winning markets
b = Net PnL
c = Commission Generated

You know b and c, c is points *.1 for the week, and you need to solve a. This won't be correct to the penny, but I don't think that's possible using only the data you provide.

For instance if b = £4000 and c = £2000

a*.02+(a*.98-4000)*.03=2000

You plug some numbers into a until you get 2000, which gives:

42915*.02+(42915*.98-4000)*.03=2000

gross winnings = £42,915
gross losses = £42,905*.98-4000=£38,056.70

Another example:

If b = -£600 and c = £4019.40

81000*0.02+(81000*0.98+600)*0.03=4019.40

gross winnings = £81,000
gross losses = £79,980

Hopefully someone else will show how to solve 'a' more elegantly than plugging in some numbers [;)]

Indeed, just total the commission paid from the account history and add it on.