P(all 3 passed) = (2/3)(5/8)(3/4)

P(none passed) =  (1-2/3)(1-5/8)(1-3/4) = (1/3)(3/8)(1/4) = 1/32

P(exactly 2 passed) = 

P(1st and 2nd passed but 3rd did not pass) +
P(1st and 3rd passed but 2nd did not pass) +
P(2nd and 3rd passed but 1st did not pass) =

(2/3)(5/8)(1-3/4) + (2/3)(1-5/8)(3/4) + (1-2/3)(5/8)(3/4) =

(2/3)(5/8)(1/4) + (2/3)(3/8)(3/4) + (1/3)(5/8)(3/4) = 43/96

Edwin

(a)  all the three boys passed:                             P = .



(b)  the probability that none of the three boys  passed:   P = .



(c)  the probability that only two boys passed:             P =  +  + .