How to force oracle to use index range scan?

Question

I have a series of extremely similar queries that I run against a table of 1.4 billion records (with indexes), the only problem is that at least 10% of those queries take > 100x

Answer 1

I have seen hint is ignored by Oracle.

Recently, our DBA uses "optimizer_index_cost_adj" and it utilized the index. This is Oracle parameter but you could use it as session level.

100 is default value and we used 10 as the parameter.