Ans. 6720

Sol. Let us name the rings as r 1 , r 2 , r 3 , r 4 and r 5 . The ring r 1 can be placed in any of the 4 fingers . . .

∴ There are 4 different ways to place ring r 1 . After placing r 1 , we have 5 choices of placing r 2 , since for the finger which holds r 1 , we have choice to place r 2 below or above r 1 . Similarly r 3 (r 4 ) [r 5 ] can be placed in 6(7) [8] ways. Thus the total number of ways to arrange 5 distinct rings on 4 fingers of left hand is (4) (5) (6) (7) (8) = 8!/3! = 6720.