Miss rate of Read = 0.3 and Hit rate of Read = 0.7
Miss rate of Write = 0.4 and Hit rate of Write = 0.6
50% are read requests and rest 50% are write requests.
Cache Memory Access time = 10ns and MM access time = 460ns.
Average Memory Access time when using Write Through protocol
$= 0.5(0.7(10) + 0.3(10 + 460))ns + 0.5(0.6(460) + 0.4(460))ns = 304ns$
Average Memory Access time when using Write Back protocol
$= 0.5(0.7(10) + 0.3(10 + 460))ns + 0.5(0.6(10) + 0.4(10+460))ns = 171ns$