hit ration h=0.8 the miss ratio =0.1
since it is write through
so avg access time = h*cache access time + (1-h)*(cache access time+main memory access time)
for only read cycles :
0.8*((0.9*100)+0.1*(100+1000)) = 0.8 * 200 =160
for only write :
0.2*((0.9*100)+0.1*(100+1000)) = 0.2 * 200 =40
for both read and write :
avg access time = 160 + 40
=200