Difficulty: Easy
Correct Answer: 9 : 90
Explanation:
Introduction / Context:11 × 12 = 132, suggesting the rule f(n) = n * (n + 1). We must select the pair that satisfies this mapping in the same form.
Given Data / Assumptions:
Concept / Approach:Test each option.
Step-by-Step Solution:
9 × 10 = 90 ✔10 × 11 = 110 ≠ 100 ✗13 × 14 = 182 ≠ 169 ✗ (169 = 13^2)15 × 16 = 240 ≠ 250 ✗14 × 15 = 210 ≠ 196 ✗ (196 = 14^2)Verification / Alternative check:Only “9 : 90” maintains n*(n+1).
Why Other Options Are Wrong:They reflect n^2 or mismatched products.
Common Pitfalls:Confusing square with pronic (n*(n+1)) numbers.
Final Answer:9 : 90
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