There are 30 devices, it is known that 20 of them are failure and 10 are ok. There are chosen 4 of them. What is the probability that the chosen devices are not all of them failure/ok?
res. p = 0.611
OK so I tried finding the prob. that 4 of them are failure. I think it is So the required prob. must be . Is it wrong? hehe obviously the res. is different