Question 1102406
Each question has a 0.25 probability of being right
Want 12 or more right
start with 12, 20C12(0.25^12)(0.75^8)=0.0008

20C13*0.25^13*0.75^7=0.0002-- both are 0.0009 if the rounding is done only at the end.
20C14*0.25^14*0.75^6=0.000026
Probability is 0.0009
Expected value is 5, np, and variance is 5(.75)=3.75, so sd is sqrt (3.75)=1.94, so this is about 3.5 sd s from mean of 5.