Past records show that 80% of the operations performed by a certain doctor were successful. If the doctor performs 4 operations in a day, what is the probability that at least 3 operations will be successful?
The probability that the operations performed are successful is = 0.8
The probability that at least three operations are successful is = P(3) + P(4)
⇒ 4C3(0.8)3(0.2)1 + 4C4(0.8)4(0.2)0
⇒ 
1