In the bitmap approach " every disk block will map with one binary bit (not matter it is free or not)"
total no of disk blocks=disk size/one disk block size = 80GB/8KB =10M
now one disk block contains 64 K bits so it contains info (free /busy) about 64K disk blocks.
so for 1 M blocks = 10M/64K=160 disk blocks.{--ans}