There are 2 ways of accessing the memory, one being simultaneous memory access and the other being hierarchical.
Simultaneous--> T(avg) = H1 T1 + (1-H1) T2
Hierarchical--> T(avg) = H1 T1 + (1-H1) (T2+T1)
When nothing is mentioned we will use Hierarchical by default as it helps in better spatial locality by bringing an entire block in the cache.