Answer for last question in Module 8 is wrong.

Question

What would be matched by "(4{5,6})\1"?
this would mean 5 or 6, 4s correct? (44444 or 444444)
However, when clicked it answers WRONG, it denotes that "10 or 12 fours" is the correct
answer.
If that were true, the question would be What would be matched by "(4{10,12})\1"?
Am I wrong about this???

Answer 1

The given answer is correct. (4{5,6}) matches 44444 or 444444. However, \1 says "one repetition of group one", so it matches 10 or 12 fours.

You might find the chapter about special sequences useful.

Answer 2

\1 means one repetition of the group it is succeeding group...
The first group should be 5 or 6, 4s.
Then its repeated again for the special sequence \1.
So no of fours doubles.. (4{10,12})\1.is the right answer.