Cache Updation Ploicies- Write back and Write through

CO- Cache Updation Policies


Consider a cache with Hit ratio for a read=0.8, Hit ratio for a write=0.9, Time to access cache =10ns, time to access main memory=100ns.

Whenever there is a miss (read/write) a 2-word block must be transferred from main-memory to cache. Let frequency of read=80%

1) What is the avg access time(both read and write) with write-through policy

2)if the cache is initially full such that at any time it contains 30% dirty blocks. What is the average access time(both read and write) in Writeback


Please elaborate clearly. Have confused.....