Question

Find the number of ways of putting five distinct rings on four fingers of the left hand. (Ignore the difference of size of rings and the fingers)

• A. 1250
• B. 6720
• C. 5260
• D. none of these

Answer 1

The correct option is B 6720

Since rings are distinct, hence they can be named as $R_1,R_2,R_3,R_{4}and{R}_5.$
The ring $R_1$ can be placed on any of the four fingers in 4 ways. The ring $R_2$ can be placed on any of the four fingers in 5 ways since the finger in which $R_1$ is placed now has 2 choices, one above the $R_1$ and one below the ring $R_1$.
Similarly $R_3$, $R_4$ and $R_5$ can be arrange in 6, 7 and 8 ways respectively.
Hence, the required number of ways
$=4\times 5\times 6\times 7\times 8=6720$