Answer: 60% or 0.6
Explanation:
The probability of event X is 50% or 0.5, and the probability of event Y is 10% or 0.1. When events X and Y are mutually exclusive, it means that they cannot both occur at the same time. 
Therefore, the probability of event X or Y occurring is the sum of their individual probabilities. 
To find the probability of X or Y, we add the probabilities of X and Y together: 
0.5 + 0.1 = 0.6 
So, the probability of event X or Y occurring is 0.6, or 60%. 
Therefore, the correct answer is not 10%, but 60%.