Question 1047170
See them both days is 0.81*0.81=0.6561
See them on at least one day is 1-not seeing them at all=1-(0.19^2)=0.9639
To have a 97% probability of seeing them at least once, then need less than or equal to 0.03 probability NOT to see them at all.  0.19^x=0.03
take logs of both sides
x log (0.19)=log (0.03)
x=log (0.03)/log(0.19)=2.11 days.  That rounds up to 3 days, which would have been suspected from the answer to (b).