Answer: 1/3
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Explanation:
A = multiples of 5 between 1 and 30
A = {5,10,15,20,25,30}
B = multiples of 6 between 1 and 30
B = {6,12,18,24,30}
There are 6 items in set A and 5 items in set B. This gives 6+5 = 11 items overall; however, notice that "30" shows up twice. So we have to subtract off 1 to account for this. This means there are 11-1 = 10 unique values that are either a multiple of 5, a multiple of 6, or a multiple of both. This is out of 30 numbers in the set {1, 2, 3, ... , 29, 30}
The probability we want is 10/30 = 1/3
