Solved the issue - for anyone who wants to know for the future...
Code:
No_probe_vehicle = 20 # number of trials
Speedarray = ([30,30,30,30,40,40,40,40,50,50,50,50,60,60,60,60])
for j in range (0,No_probe_vehicle):
probe_speed = random.choice(Speedarray)
Speed[1] = probe_speed*(1609.44/3600)
print "Probe Speed", probe_speed
print "Speed Array", Speedarray
Speedarray.remove(probe_speed)
print "speed", Speed