SOLUTION: How to find the probability of matching 4 out of 5 numbers from a lottery with number 1 to 45

There are 5 numbers that match the winning set and 40 which don't

P(matching exactly 4 and mismatching 1)

The number of ways to choose the 4 matching ones is C(5,4) 

For each of those C(5,4) ways to choose the 4 matching ones,
there are C(40,1) ways of choosing the nonmatching one.

So there are C(5,4)*C(40,1) ways to choose exactly 4 matching ones
and exactly one non-matching one.

There are C(45,5) ways of choosing ANY 5

So the probability is

 C(5,4)*C(40,1)       5*40        200
---------------- = --------- = --------- = .0001636984053
    C(45,5)         1221759     1221759


Not too likely.  Studying math teaches you that gambling 
without using skill to put the probability of winning in 
your favor is never wise.

Edwin