Date narrowing – Meeta remembers her father's birthday is after 8 July but before 12 July. Her brother remembers it is after 10 July but before 15 July. On which day in July is the birthday definitely?
Verbal Reasoning
Time Sequence
Difficulty: Easy
Choose an option
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A10th
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B11th
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C10th or 11th
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DCan't be determined
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E12th
Answer
Correct Answer: 11th
Explanation
Introduction / Context:We are intersecting two open intervals described in words. One memory gives (8, 12), the other gives (10, 15). The definite day is their intersection.
Given Data / Assumptions:
- After 8 July but before 12 July → possible dates: 9, 10, 11.
- After 10 July but before 15 July → possible dates: 11, 12, 13, 14.
Concept / Approach:Compute the set intersection of the two candidate sets.
Step-by-Step Solution:
Set A = {9, 10, 11}.Set B = {11, 12, 13, 14}.A ∩ B = {11}.Verification / Alternative check:Check boundary words carefully: “after” excludes the boundary day; “before” also excludes the boundary. That is why 8 and 12 are excluded from Meeta's set, and 10 and 15 from the brother's set.
Why Other Options Are Wrong:
- 10th: Not in the brother's range.
- 10th or 11th / Can't be determined: Intersection is a single value (11).
- 12th: Not in Meeta's range.
Common Pitfalls:Including endpoints despite the word “after/before”; treating “between” inclusive. Read quantifiers precisely.
Final Answer:11th