The outcome A="At least one" means {1,2,3,4,5......n} where n is the maximum possible outcome.
The only other outcome (B) left (i.e. the complement of the above event "at least one") is (B)={0}.
Therefore, by Kolmogorov's second axiom, A and B are complements, and
P(A)+P(B)=1
therefore
P(A)=1-P(B), or in words,
Probability of outcomes of "at least one" is the complement of the outcome of "0" item.
37 and 29 won't work because these numbers are prime numbers, which can't be divided equally. This problem is basically saying which one of these are prime numbers.
Answers are: A, C, D
Note how
(3/20)*20 = 0.15*20 = 3
0.15*20 = 3
(15/100)*20 = 0.15*20 = 3
all expressions lead to the same result of 3
another thing to notice
3/20 = 15/100 = 0.15 = 15%
which are multiple ways to say the same thing just in a different form
