In 2000yr, number of odd days =0 Now in 8yr, two are leap years. ∴ Number of odd days in 8yr ‌‌=6×1+2×2=10 ‌‌=3‌ odd days ‌ Now, from 1 Jan 2009 to 31 Jan 2009 , Number of odd days =3 ∴ Total odd days =3+3=6 and required day = Saturday