1 - 0.05^3*0.95^147*150!/(3!*(147!)) +
0.05^2*0.95^148*150!/(2!*(148!)) + 0.05^1*0.95^149*150!/(1!*(149!)) +
0.05^0*0.95^150*150!/(0!*(150!)) = 0.981538
So the chance of rolling 4 or more natural 1's is 98.15 %
The chance for exactly 4 natural 1's is 0.05^4*0.95^146*150!/(4!*(146!))...