A code is to be made by arranging 7 letters. Four of the letters used will be the letter A, one of the letters used will be the letter B, one of the letters used will be the letter C, and one of the letters used will be the letter D. If there is only one way to present each letter, how many different codes are possible?  Select the correct option:
A) 42
B) 210
C) 420
D) 840
E) 5,040
we have 7 letters out of which 3 are of one kind, 2 are of another kind..   so total ways = 7!/3!1!=840   ans 840
<result>D</result>
A code is to be made by arranging 7 letters. Four of the letters used will be the letter A, one of the letters used will be the letter B, one of the letters used will be the letter C, and one of the letters used will be the letter D. If there is only one way to present each letter, how many different codes are possible?