about clustered table or clustered index I/O

[Piao songmei]

for example,
there's a table R. B(R)(block count)=1000, T(R)(tuple count)=20000, and there's index on attribute a. then, how about the I/O cost for

select * from R where a=0

case1: table R is not clustered and do not use index
case2: V(R,a)=10 and index is not clustered.

my answer VS. book:
case1: I/O=1000 VS. I/O=20000
case2: I/O=1000 VS. I/O=2000

how about you?