A 4-letter code word consists of letters D, E, and G. If the code includes all the three letters, how many such codes are possible? Choose the most appropriate option.
A) 72
B) 48
C) 36
D) 24
E) 18
Note that the correct answer to this question is 36, not 72.   D-DEG can be arranged in 4!/2!=12 ways;   E-DEG can be arranged in 4!/2!=12 ways;   G-DEG can be arranged in 4!/2!=12 ways;   Total:  12+12+12= 
<gadget id="calculator"> 12+12+12</gadget>
<output>36</output>
36.   Answer: 36.
<result>C</result>
A 4-letter code word consists of letters D, E, and G. If the code includes all the three letters, how many such codes are possible?