In the mixed ascending and descending alphabet series CDE, IHG, KLM, QPO, STU, which of the following three-letter groups should come next?

Introduction / Context:
This alphabet-series question mixes ascending and descending sequences. Some triplets move forward through the alphabet, while others move backward. The candidate must detect both the order (ascending or descending) and the change in the starting letters. Such questions are useful for testing both observation skills and logical consistency in pattern recognition.

Given Data / Assumptions:

• Given series: CDE, IHG, KLM, QPO, STU, ?.• CDE, KLM and STU are clearly in alphabetical order.• IHG and QPO are in reverse alphabetical order.• Starting letters are: C, I, K, Q, S and then an unknown letter.

Concept / Approach:
First, we classify each term as ascending or descending. Next, we consider the pattern formed by the first letter of each triplet. If the first letters follow a regular increment, we can predict the next starting letter. We then decide whether the next term should be in ascending or descending order by observing the alternating pattern of directions across the series.

Step-by-Step Solution:
CDE is ascending (C, D, E), IHG is descending (I, H, G).KLM is ascending (K, L, M), QPO is descending (Q, P, O).STU is ascending (S, T, U). We see a repeating pattern: ascending, descending, ascending, descending, ascending.Therefore, the next term should be descending.Now consider first letters: C=3, I=9, K=11, Q=17, S=19.The pattern for first letters is +6 (3→9), then +2 (9→11), then +6 (11→17), then +2 (17→19). So the next step should again be +6.19 + 6 = 25 which is Y, so the final term must start with Y and be a descending sequence.A descending triplet starting at Y is YXW.

Verification / Alternative check:
The series of first letters is C, I, K, Q, S, Y which corresponds to 3, 9, 11, 17, 19, 25 and follows the +6, +2 repetition. For the direction pattern, we have ascending, descending, ascending, descending, ascending, descending. Only YXW is both descending and begins with Y. Thus the choice fits both the direction alternation and the numeric increment rule.

Why Other Options Are Wrong:
WXY, XYW and XWY either start with the wrong first letter or do not follow a strictly descending order. WXY is ascending, while XYW and XWY either mix ascending and descending in an irregular way or begin with X rather than Y. Since both the starting letter and the direction are fixed by the pattern, these options cannot be accepted.

Common Pitfalls:
A typical mistake is to ignore the alternation between ascending and descending triplets and look only at the first letters. Another is to miscalculate the numeric jumps between first letters. Careful separation of the two aspects, direction and starting point, helps avoid confusion and ensures a logical solution.

Final Answer:
YXW