The letters D, G, I, I , and T can be used to form 5-letter strings as DIGIT or DGIIT. Using these letters, how many 5-letter strings can be formed in which the two occurrences of the letter I are separated by at least one other letter?
Choose the correct choice from the following choices.
A) 12  B) 18  C) 24  D) 36  E) 48
Total no of ways arranging 5 letter with one letter redundant is 5!/2!=60   No of ways two I's can be together 4!=24   no of ways at least one alpha is between two I's =60-24= 
<gadget id="calculator">60-24</gadget>
<output>36</output>
36   ANS:36
<result>D</result>
The letters D, G, I, I , and T can be used to form 5-letter strings as DIGIT or DGIIT. Using these letters, how many 5-letter strings can be formed in which the two occurrences of the letter I are separated by at least one other letter?