That’s a nice idea but unfortunately I don’t think the calculation’s quite that simple.
My understanding is that ballot will select users who pledged at random. Each user’s pledge will then be deducted from the amount that was allocated for CrowdCube investors to invest & once the total allocation = the pledges of everyone who was chosen at random, that’s it.
So obviously if every person who’s selected has pledged £1,000 (though the amount you pledge does not impact your chance of being chosen), fewer users will have the chance to invest than if every person who’s selected has pledged £10.
On top of that, if the users who are selected don’t invest the full amount that they pledged (& I expect that will be what happens), Monzo will repeat this process until the total allocation is used up. So even if you use the average pledge from the presentation to calculate the likelihood of being able to invest, as I did here -
in reality, the odds are probably better.