How many such three letter passwords can exist? Choose one:
A) 216
B) 26C6 *3
C) (26C6)^3
D) ((26C6)^3) *63
E) 215
1st ring: 6 out of 26 alphabets can be selected in 26C6 ways.   And is for 2nd and 3rd ring.   Also, these 3 set of 6 letters can be arranged amongst themselves in 63 ways.   Hence, total number of 3 letter passwords = 26C6 * 26C6 *26C6 *63 ways.   ANSWER:((26C6)^3) *63
<result>D</result>
How many such three letter passwords can exist?