Question: what are the country id ? | Did  you  mean country id which has both roller coasters with speed higher than 60 and roller coasters with speed lower than 55? | Yes!
SQL: SELECT T1.Country_ID FROM country AS T1 JOIN roller_coaster AS T2 ON T1.Country_ID  =  T2.Country_ID WHERE T2.speed > 60 INTERSECT SELECT T1.Country_ID FROM country AS T1 JOIN roller_coaster AS T2 ON T1.Country_ID  =  T2.Country_ID WHERE T2.speed < 55