We must use this formula: n! / [r! * (n-r)!]
40! / 6! * 34! = (40 * 39 * 38 * 37 * 36 * 35) / 6! which equals
2,763,633,600 / 720 = 3,838,380 ways you can choose 6 numbers out of forty.
So, the probability of winning equals 1 / 3,838,380 whch equals
0.00000026052657631605
Source: 1728.com/combinat.htm