I have given this formula before but I don't know how to direct you there so I have presented it again below:

Let C=the prob of at least 1 win from n races, called the certainty, expressed as a decimal.
Let q=the prob of a LOSS in a race, expressed as a decimal (i.e. 1-win strike rate).

Now to be 100% certain you need an infinite number of races so this theory expects you to decide on an acceptable certainty usually 90% or 95% of getting at least one winner from n races.

The number of expected outs is given by n from

n=log(1-C)/log q

You can use log or ln on your calculator or spreadsheet but it has to be the same throughout the calculation.

For example, consider top place percent which Knowles suggests has a 22% strike rate (q=1-0.22=0.78) and deciding on 95% certainty (C=0.95) then,

n=log(1-0.95)/log 0.78
n=log 0.05/log 0.78
n=12.06 so you can be 95% sure of at least one winner in about 12 races.

To be 99% sure it takes a run of about 18 or 19 races.

gunny72