In how many ways can a four-letter password be chosen, using the letters A, B, C, D, and/or E, such that at least one letter is repeated within the password? Pick
A) 505  B) 864  C) 900  D) 936  E) 1,296
Total number of four letter passwords = 5*5*5*5= 
<gadget id="calculator">5*5*5*5</gadget>
<output>625</output>
625 ------(1)   Total number of passwords in which no letter repeats= 5C4*4!= 5*24= 
<gadget id="calculator">5*24</gadget>
<output>120</output>
120------(2)   therefore required value= (1)-(2)= 625-120= 
<gadget id="calculator">625-120</gadget>
<output>505</output>
505   505
<result>A</result>
In how many ways can a four-letter password be chosen, using the letters A, B, C, D, and/or E, such that at least one letter is repeated within the password?