v = Variables[exp];
Prepend[N[
Append[v, exp] /.
FindInstance[exp < 1/2 && 0 < # < 1 & /@ v , v , 20]],
Append[v, "exp"]] // MatrixForm
One way to restrict the results to even 10's is to round and then double check we still meet the criterea.
TableForm[
Sort@Select[Join[#, {(exp /. Rule @@@ Transpose[{v, #}])}] & /@
Union[
Round[v /.
FindInstance[(exp /. Subscript[R, n_] :> Subscript[R, n]) <
1/2 &&
0.05 < # < .95 & /@ v , v , 20], .1]] , Last[#] < .5 &],
TableHeadings -> {None, Join[v, {"exp"}]}]
