Half the characters have the initial A, which is a total of 60 / 2 = <<60/2=30>>30 characters.
This means that 30 / 2 = <<30/2=15>>15 characters have the initial C.
Mary wants the remaining 60 – 30 – 15 = <<60-30-15=15>>15 characters to have the initials D or E.
For there to be twice as many characters with the initial D, the characters are divided into 2 + 1 = <<2+1=3>>3 parts.
Dividing by this means there are 15 / 3 = <<15/3=5>>5 characters with the initial E.
This leaves 15 – 5 = <<15-5=10>>10 characters with the initial D.
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