In how many ways can a three-letter password be chosen, using the letters A, B, C, D, E, and/or F, such that at least one letter is repeated within the password?  Choose the correct choice from the following options:
A) 72
B) 86
C) 90
D) 96
E) 1,296
Total number of four letter passwords = 6*6*6= 
<gadget id="calculator">6*6*6</gadget>
<output>216</output>
216 ------(1)   Total number of passwords in which no letter repeats= 6C3*3!= 20*6= 
<gadget id="calculator">20*6</gadget>
<output>120</output>
120------(2)   therefore required value= (1)-(2)= 216-120= 
<gadget id="calculator">216-120</gadget>
<output>96</output>
96   96
<result>D</result>
In how many ways can a three-letter password be chosen, using the letters A, B, C, D, E, and/or F, such that at least one letter is repeated within the password?