FLC OF LTT LANDS ON WRONG RWY WHEN NEW RWY OPENED BUT NOT NOTED ON ATIS.

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THE CAPT LEFT THE FREQ TO GET ATIS. WHILE HE IS OFF I WAS CLRED TO 8000 FT. WHEN CAPT RETURNED HE SAID BMI USING VOR-DME 21 CIRCLE 20 APCH; AND RWY 11/29 CLOSED. WE BOTH LOOKED AT ARPT DIAGRAM AND SAW RWY 21 BUT NOT RWY 20. WE WERE BOTH PUZZLED. THERE WAS A RWY UNDER CONSTRUCTION ON OUR DIAGRAM; BUT NO INDICATION OF WHAT RWY IT WAS; IE RWY 20; RWY 19; RWY 8 OR IF IT WAS FINISHED. THE ATIS DID NOT MENTION ANYTHING ABOUT A NEW RWY BEING OPENED. CAPT DISTRACTED ME BY ASKING IF I HAD THE CURRENT CHARTS WHICH WE BOTH DID. AND BY DETERMINING IF WE HAD LNDG PERFORMANCE TO LEGALLY LAND ON RWY 21 WHICH WAS 3723 FT LONG; WHICH WE ALSO HAD. CAPT LEFT FREQ AGAIN TO TALK TO BMI TWR AND DISPATCH. WHILE HE WAS OFF; I WAS CLRED TO 5000 FT; THEN 2500 FT AND TOLD TO CONTACT BMI APCH. BMI APCH CLRED ME TO 2400 FT AND INTERCEPT VOR-DME 21 APCH COURSE. WHEN CAPT RETURNED I CALLED FOR DSCNT AND APCH CHKS. CAPT PERFORMED BOTH. WHEN HE CAME TO THE ARPT BRIEF PART; I ASKED HIM IF HE WANTED ME TO BREAK OFF THE APCH. HE SAID; 'NO; WE'RE ALL SET UP.' SO I CONTINUED. WITH LITTLE DISCUSSION WE BOTH CONCLUDED THAT RWY 21 HAD BEEN RENUMBERED RWY 20. I ASSUMED CAPT HAD CLARIFIED THIS WHEN HE TALKED TO TWR EARLIER. HE APPARENTLY DIDN'T ASK ABOUT RWY 20; INSTEAD ASKED ABOUT RWY 11/29. I MADE A NORMAL; UNEVENTFUL LNDG ON RWY 21. TWR NEVER SAID ANYTHING TO US AS WE TAXIED IN AND PARKED. THE CAPT AND I DISCUSSED OUR CONFUSION OVER RWY 20; WHEN HE NOTICED A RWY DIRECTION SIGN ON THE RAMP AND NOTICED RWY 20 AMONG THE 6 RWYS SHOWN. THE CAPT TALKED TO BOTH TWR SUPVR AND STATION PERSONNEL. THE TWR SUPVR SAID THEY WERE DISTR BY ANOTHER PLANE THAT WAS LOST; AND DIDN'T SEE US LAND ON RWY 21. IN FACT; THEY JUST LAUGHED AND SAID DON'T WORRY ABOUT IT; OR SO SAID THE CAPT. STATION PERSONNEL SAID RWY 20 HAD BEEN OPEN ONLY 1 1/2 HRS BEFORE OUR ARR. WE RECEIVED NO NOTAMS FROM DISPATCH; STATION; ATIS; TWR; OR EVEN OUR 'CHART NOTAMS' ABOUT THIS NEW RWY 20 BEING OPENED TODAY. OF THE MANY MISTAKES THAT OCCURRED IN THIS INCIDENT; THE BIGGEST MISTAKE WAS NOT BREAKING OFF THE APCH WHEN I MENTIONED IT TO THE CAPT. IN THE FUTURE TO PREVENT THIS FROM HAPPENING; THE SOLUTION IS TO ASK 'STUPID' QUESTIONS; IE; 'WE DON'T SHOW A RWY 20 ON OUR CHARTS.' OR; 'IS RWY 21 RENUMBERED 20?' WITH ALL THE RESOURCES WE HAD AVAILABLE; WE CHOOSE TO COMPLICATE MATTERS RATHER THAN SIMPLIFY THEM WITH A SIMPLE 'STUPID' QUESTION. OTHER FACTORS THAT MAY HAVE AFFECTED QUALITY OF HUMAN PERFORMANCE. 1) ON DUTY 10 HRS BEFORE HAVING OPPORTUNITY TO EAT FOOD (PRETZELS AND COKE NOT A SUBSTITUTE FOR FOOD). 2) LEG 6 OF A 7 LEG DAY ON DAY 4 OF 4 DAY TRIP MAKES ONE TIRED; BUT NOT FATIGUED (I HAD ADEQUATE REST). 3) CAPT WAS INSTRUCTOR PLT WITH LITTLE RECENT LINE FLYING EXPERIENCE.