Prob of Passing Qn correct, passing, 120

rohitdoshi

As a break from Level 2 study:

Each Qn has 3 choices and there are a total of 120 Questions in CFA Level 2 exam. If a candidate can answer 70 % of Qns (82 correct answers out of 120 questions), he/she is deemed to be passed. What is the probability of a candidate passing if all questions are answered randomly.

huangxiaoxie

Whatever it is, it's not zero.

mp3bu

corr incorr nCr P(X=x)
84 36 5.42594E+30 2.07493E-16
85 35 2.29804E+30 4.39398E-17
86 34 9.3525E+29 8.94123E-18
87 33 3.655E+29 1.74714E-18
88 32 1.37063E+29 3.27588E-19
89 31 4.92809E+28 5.88922E-20
90 30 1.69745E+28 1.01426E-20
91 29 5.596E+27 1.67185E-21
92 28 1.76396E+27 2.63498E-22
93 27 5.31084E+26 3.96664E-23
94 26 1.52545E+26 5.69677E-24
95 25 4.17493E+25 7.79557E-25
96 24 1.08722E+25 1.01505E-25
97 23 2.69003E+24 1.25573E-26
98 22 6.31333E+23 1.47356E-27
99 21 1.40296E+23 1.63729E-28
100 20 2.94622E+22 1.71915E-29
101 19 5.8341E+21 1.70213E-30
102 18 1.08674E+21 1.58532E-31
103 17 1.89917E+20 1.38523E-32
104 16 3.10441E+19 1.13216E-33
105 15 4.73052E+18 8.62598E-35
106 14 6.69414E+17 6.10329E-36
107 13 8.75868E+16 3.99281E-37
108 12 1.05429E+16 2.40308E-38
109 11 1.16068E+15 1.3228E-39
110 10 1.16068E+14 6.61398E-41
111 9 1.04566E+13 2.97927E-42
112 8 8.40262E+11 1.19703E-43
113 7 59487568920 4.23726E-45
114 6 3652745460 1.30091E-46
115 5 190578024 3.39369E-48
116 4 8214570 7.31399E-50
117 3 280840 1.25025E-51
118 2 7140 1.58931E-53
119 1 120 1.33555E-55
120 0 1 5.5648E-58

Sum = 2.6252E-16


Wouldn't try it...

tikfed

If you raise the 33% possibility of randomly answering any given question correctly to the 82nd power for the number of questions you need to "guarantee" passing, you will see 40 zeros after the decimal point before you hit your first glimpse of possiblilty...I would say that the t-stat proving the correlation between this method and not passing is upwards of 1,000,000

stalkey

but that is the probability of getting consecutive right answers...

Swanand

Yeah you're right, but even with 38 extra questions, I doubt that the chances improve too much! I think that statistically, b is the most common answer choice in multiple choice exams...I would go with that instead of complete random answers.

OmarAdnan

so the final answer... The probability of guessing 84 or more questions correct...

P(x>83)= 0.0000000000000262519983865%

bolligerallstar

Kevin,
I am pretty much in the same boat though for different reasons. Good to have some company )
I started studying in Apr and joined a new team immediately after that..since than its 65-70hrs working weeks..but i think i wouldn't have to guess all the Qs..