Bill's statement does not make sense because it is incorrect:
7/12 customers bought pretzels 3/10 OF those customers bought low salt pretzels (x) 3/10 of 7/12 = x (the word "OF" normally refers to multiplication and he variable x represents low salt pretzels) 3/10 times 7/12 = x 21/120 = x Simplify: 7/40
To be correct, Bill would have to say that 7/40 of the customers bought low salt pretzels, but instead he had said 7/30.