Basically, if you want to find the probability of getting either outcomes, you will need to subtract the probability of getting neither outcomes in the question. The probability for both outcomes are 7/9 and 5/9 respectively. You will have to multiply to get the probability of getting both of the non-desired outcomes. Hence, it gives the equation above
Well, the answer would bee 1/10 for a simple reason: the 3 in 7.315 is in the tenth's spot while the 3 in 893.5 is in the ones. a one spot different that can be proven with logic.