Difficulty: Medium
Correct Answer: 9 years
Explanation:
Introduction / Context:Two-digit reversal problems convert naturally to digit algebra. If Mr. Manoj's age is 10a + b and his wife's age is 10b + a, we can model the sum and difference, apply the given relation, and solve for permissible digit pairs (a, b) with a > b because Manoj is older.
Given Data / Assumptions:
Concept / Approach:Compute sum S = 11(a + b) and difference D = 9(a − b). The condition (1/11)S = D reduces to a single linear relation between a and b. Solve for integer digits then compute the age difference.
Step-by-Step Solution:
S = (10a + b) + (10b + a) = 11(a + b)D = (10a + b) − (10b + a) = 9(a − b)(1/11)S = D ⇒ a + b = 9(a − b)⇒ 10b = 8a ⇒ b = 0.8aDigit pair with a > b: a = 5, b = 4 works (others non-digit or invalid)Ages: Manoj = 54; wife = 45 ⇒ difference = 9 yearsVerification / Alternative check:Check the condition: sum = 99; (1/11)*99 = 9 equals difference 9. All constraints satisfied.
Why Other Options Are Wrong:10/8 years do not meet the algebraic constraint; “Cannot be determined” is false because the digits are uniquely pinned to 5 and 4 under the given condition.
Common Pitfalls:Forgetting that leading digit a cannot be 0; ignoring the older/younger condition which enforces a > b.
Final Answer:9 years
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