AE VR Book 1, exercise 1 : 2b q10 - wrong answer?

[Stroller]

Write the two missing letters:

DU FD FS HA IP KY _ _

We made it to ML as a plausible answer, but the "correct" answer provided is KN and we just can't see how to get there from the question. What are we missing? Or is there a mistake (in either the question or the answer)? I tried searching previous posts, but couldn't see any, so all help would be appreciated.

[Falls into the minor, but baffling, category ]

[Sally-Anne]

DU FD FS HA IP KY _ _

It's a very poorly written question.

As you've fathomed, the only pairs that are relevant to the answer are 1, 3 & 5, so you are working with:

DU FS IP _ _

To get to the answer KN:

- the first pair is +2, +3 ... +2
- the second pair is -2, -3 ... -2

The trouble is that the question really doesn't give you sufficient information to be certain of that. It could just as easily be +2, +3 ...+4, and -2, -3 ... -4, giving the answer ML.

To give a clear pattern, another two pairs of letters should have been provided.

[Tagore]

Hi Stroller,
Since you have ML as a possible answer, the two separate sequences have been recognised. Look at the first sequence independently ….

DU FS IP ….. D to F is a jump of 2 and F to I is a jump of 3 so it is natural to think that the next jump would be 4, resulting in M as the first letter. However, what if the jumps were 2, 3, 2, 3 alternating? This would result in KN as the next set of letters. I hope this was an MC question.

It’s been a while since we looked at this so my reasoning maybe subject to challenge.
Tagore

[Stroller]

Thanks, Sally-Anne and Tagore, for putting me out of my misery. At least I can see how you got there now, but - left to my own devices - I would have been satisfied with ML without thinking of alternate answers and explanations.

Tagore, no, it wasn't multiple choice. I wish questions were written and tested to avoid such ambiguity...