Chapter 7 - Section 7.5 - Conditional Probability and Independence - Exercises - Page 507: 27

Mutually exclusive

Here, both $A$ and $B$ are mutually exclusive events because $A \cap B=0$. This means that both $A$ and $B$ cannot occur at the same time of any event because new skateboard design cannot be both succeeded and failure at the same time. Thus, both $A$ and $B$ are mutually exclusive.