Understanding the Unders/Overs bet

[London_Calling]

EDITED - I've tried to make the workings clearer Not looked at this before but came up with an idea a few weeks ago, and want to make sure I'm understanding the mechanics of the Unders/Overs bet. Only have 72 results from the Championship (it's a ridiculously small sample) but as I say, it's the mechanics of a bet that's new to me that I wanted to check. Of the 72 matches, 52 are qualifiers - if you have a moment, could someone have a look at my thinking: Under/Over 2.5 goals: System identifies both Overs and Unders, so I presume I have 4 punting options: 1) System identifies Unders, Back Unders 2) System identifies Overs, Back Overs 3) System identifies Unders, Lay Overs 4) System identifies Overs, Lay Unders Average Unders price = 1.75 (guessing) Average Overs price = 2.1 (guessing) 72 matches: 52 qualifiers Prediction of 30 Unders - RESULT: 20 Unders/Wins, 10 Overs/Losers Prediction of 22 Overs - RESULT: 12 Overs/Wins, 10 Unders/Losers Staking Plan - no idea, assuming a flat £100 a match. So, going through the 4 optons (above) 1) Stake: 30 x £100 = £3,000 Return: 20 x (£100 x 1.75) = £3,500/ROI: 16.66% 2) Stake: 30 x £110 = £3,000 Return: 20 x (£100 x 2.10) = £4,200/ROI: 40% 3) Stake: 22 x £100 = £2,200 Return: 12 x (£100 2.1) = £2,520/ROI: 14.5% 4) Stake: 22 x £100 = £2,200 Return: 12 x (£100 x 1.75) = £2,100/ROI: -4.5% Does that make much sense at all, am I on the right track ? Cheers!