In a three level memory hierarchy, the access time of cache, main and virtual memory is 5 nano-seconds, 100 nano-seconds and 10 milli-seconds respectively. If the hit ratio is 80% for the cache and 99.5% for the main memory, then the closest average access time of memory hierarchy in nano-seconds is:

In a three level memory hierarchy, the access time of cache, main and

1.	In a three level memory hierarchy, the access time of cache, main and virtual memory is 5 nano-seconds, 100 nano-seconds and 10 milli-seconds respectively. If the hit ratio is 80% for the cache and 99.5% for the main memory, then the closest average access time of memory hierarchy in nano-seconds is:
A.	512
B.	1024
C.	10024
D.	128
Answer» D. 128