A clock strikes 1 at 1 o'clock, 2 at 2 o'clock, …, 12 at 12 o'clock. How many total strikes occur in 24 hours?
Aptitude
Calendar
Difficulty: Easy
Choose an option
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A78
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B136
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C156
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D196
Answer
Correct Answer: 156
Explanation
Introduction / Context:This classic tally problem counts the total number of bell strikes over a day when a clock strikes n times at n o'clock.
Given Data / Assumptions:
- In 12 hours the clock strikes 1+2+...+12.
- Pattern repeats every 12 hours.
Concept / Approach:Sum of the first 12 natural numbers, then double it for 24 hours.
Step-by-Step Solution:Sum S = 1+2+...+12 = (12*13)/2 = 78.In 24 hours: 2*S = 156.
Verification / Alternative check:List small segments (e.g., 1–3 o'clock) to see the pattern, then scale.
Why Other Options Are Wrong:78 is only half day; 136 and 196 do not match doubling the 12-hour sum.
Common Pitfalls:Forgetting to double; mis-summing 1–12.
Final Answer:156 strikes