Since the problem provides the information that each of the 5 questions has 4 answer choices, you may evaluate the probability to have 5 questions right, such that:

`P = (1/4)^5 => P = 1/1024 => P = 0.0009765625`

The probability to get exactly 4 questions right and 1 wrong may be evaluated such that:

`P = 1/4 = 0.25`

`P = 3/4 = 0.75 `

`P = C_5^1*(1/4)^4*(3/4) => P = 5*0.25^4*0.75 = 0.0146 ` (exactly 4 questions correct)