Digit-sum analogy: “1234 : 10 :: 6789 : ?” — infer the mapping from the first pair (sum of digits) and apply it to the second.

Introduction / Context:
Many number analogies reduce multi-digit numbers to a single value by applying digit-based functions such as sum, product, or alternating sums. Here, the first pair suggests a digit-sum mapping.

Given Data / Assumptions:

• 1 + 2 + 3 + 4 = 10.
• Apply the same to 6789 → 6 + 7 + 8 + 9.

Concept / Approach:
Maintain the exact same operator across both pairs (sum of digits) to preserve a valid analogy.

Step-by-Step Solution:
1) Confirm the exemplar mapping: 1234 → 10 via sum.2) Compute target: 6 + 7 + 8 + 9 = 30.3) Select 30.

Verification / Alternative check:
Digit-product or digital root would not yield 10, so the sum is the consistent choice.

Why Other Options Are Wrong:

• 20, 40, 50, 26: Do not match the digit-sum of 6789.

Common Pitfalls:
Switching to a different function for the second pair breaks analogy consistency.

Final Answer:
30