I do A and B but that is the way I learned it. Hope this helps :)
Answer:
Prob = 13/1024 = 0.0127
Step-by-step explanation:
Prob {A correct answer} = Correct option / Total options = 1/4
Prob {A wrong answer} = Wrong options / Total options = 3/4
Prob [3 answers correct] = P (3 correct ,& 2 wrong) or P (4 correct ,& 1 wrong) or P (5 correct, & no wrong)
= [ (1/4) x (1/4) x (1/4) x (3/4) x (3/4) ] + [ (1/4) x (1/4) x (1/4) x (1/4) x (3/4) ] + [ (1/4) x (1/4) x (1/4) x (1/4) x (1/4) ]
( 9/1024 ) + ( 3/1024 ) + ( 1/1024 )
13/1024 = 0.0127
