$ cat a.py
#!/usr/bin/env python
import random

N = 10000

for x in range(5):
    t = 0
    for _ in range(N):
        c = 0
        for _ in range(7):
            p = random.randint(1, 10)
            if p == 10:
                t += 1
                break
            elif p >= 6:
                c += 1
                if c == 3:
                    t += 1
                    break

    print("Trial #{}: {}/{} = {} %".format(x+1, t, N, float(100 * t)/N))
$ ./a.py
Trial #1: 8397/10000 = 83.97 %
Trial #2: 8443/10000 = 84.43 %
Trial #3: 8435/10000 = 84.35 %
Trial #4: 8450/10000 = 84.5 %
Trial #5: 8460/10000 = 84.6 %