Completing the letter series:

Question

I have been provided the following short puzzle and need help understanding the answer.

Complete the following letter series:
a_abc_ab_ _c_bb_cc_

I filled it like this: aaabcaabbbcabbccca
I had noticed there could be a pattern constructed using blocks of 7 sequential letters (XXXYZXX):

aaabcaa
bbbcabb
ccca...

However, I have been told that the correct answer is aaabcaabbbccbbccca, which differs from my answer in only one place. Please note, I am not sure about the answer. It was taken only as a reference. So please let this undermine your approach.

Can anyone help me understand what makes this answer is correct?

Ops... I counted one of the spaces in the question too (the one between the two underscores). I'll delete my comment then. — Bojidar Marinov, Oct 14 '15 at 10:35
Is there another clue in the original question that could explain why the official solution has exactly one run of length one, two and three for each of the three letters? — Marconius, Oct 14 '15 at 14:12
From where did you get the other answer. Are you sure it's not a typo in a book? — ghosts_in_the_code, Oct 15 '15 at 15:36
One thing that's interesting is that the question has 18 letters and it seems that the answer has 6 a's, 6 b's and 6 c's — Dr Xorile, Oct 15 '15 at 19:37
everytime I tried a new pattern or sequence, i always end up with A. I think @AdityaAgarwal should check if it is really C in the correct answer. — Mekalikot, Oct 16 '15 at 01:41
So, for example, all the combinations aa, ab, ac, ba, bb, bc, ca, cb, cc ordered and arranged in some clever way could form the solution — Dr Xorile, Oct 16 '15 at 02:34
@DrXorile Except that the existing series already has 'ab' twice. — Joel Rondeau, Oct 19 '15 at 14:41
They wouldn't have to be together. But I can't see it. The OP's answer is nicer. I'm just pointing out a symmetry — Dr Xorile, Oct 19 '15 at 14:53

Carl Löndahl · Accepted Answer · 2015-10-24T21:35:23.940

3

Another sequence that would make sense would be

aaa,b,c,aa,bb,cc,a,bbb,ccc,...

since

the a's decrease and the b's and c's increase in numbers.

That doesn't explain the stated correct answer, though.

edited Oct 24 '15 at 21:35

answered Oct 24 '15 at 21:29

Carl Löndahl

5,280
1
18
29

I think that was a misprint. This is the most convincing answer I got so far. – Aditya Agarwal Oct 25 '15 at 05:31

score 0 · Answer 2 · answered Oct 15 '15 at 17:27

The only thing I can think is that with the "correct" answer you get a single, double and triple sequence of all 3 letters.

triple a,
single b,
single c,
double a,
triple b,
double c,
double b,
triple c,
single a

I can't find a pattern to that though.

a,b,c,a,b,c,b,c,a

or

3,1,1,2,3,2,2,3,1

Maybe someone else sees it?

Completing the letter series:

2 Answers2