Why not 10C5 / 10C4 ? I did'nt understand how is it not combinations problem ? Number of 5 letter words can be chosen from 10 letters in 10C5 ways ??? Although I am getting the ratio to be 6/5 if use Combinations, hence it has o be incorrect. Can anyone explain pls.
ABCDE and ABCED is different codes as the problem says: "a sequence
of different letters"
Faster solution: We can create 5-letters code from 4-letters code by adding one letter of 10-4=6 letters. So, 6 to 1.
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