Answer: 420 different codes are possible.
Step-by-step explanation:
The number of possible codes can be given by
N = n!/(ra! × rb! × rc! × rd!)
Where;
n is the total number of letters in the code.
ra,rb,rc and rd are number of occurrence of A,B,C and D respectively
Given: n= 7, ra=3, rb=2, rc=1, rd=1.
Substituting the values, we have.
N = 7!/(3!×2!×1!×1!)
N = 5040/12
N= 420
