Math Problem Statement

The grandfather clock at the top of the stairs says it is now 3:20AM. In how many minutes from now will the hour and minute hand of the clock first meet each other? Please round to the nearest minute.

Solution

To solve this problem, we need to determine the time it will take for the hour and minute hands of the clock to first meet after 3:20 AM.

Step 1: Convert the current time to angles

  • Hour hand position: At 3:20 AM, the hour hand is not exactly on 3, since it has moved due to the 20 minutes that have passed.

    • Each hour represents 30 degrees (360 degrees / 12 hours).
    • So, the hour hand at 3:00 is at 3×30=903 \times 30 = 90 degrees.
    • In 20 minutes, the hour hand moves 2060×30=10\frac{20}{60} \times 30 = 10 degrees.
    • Therefore, the hour hand is at 90+10=10090 + 10 = 100 degrees.
  • Minute hand position: At 20 minutes past the hour, the minute hand is at 20×6=12020 \times 6 = 120 degrees (since each minute represents 6 degrees).

Step 2: Calculate the relative speed of the hands

  • Minute hand speed: The minute hand moves 6 degrees per minute.
  • Hour hand speed: The hour hand moves 0.5 degrees per minute.

The relative speed at which the minute hand approaches the hour hand is: 60.5=5.5 degrees per minute6 - 0.5 = 5.5 \text{ degrees per minute}

Step 3: Determine the initial angular difference

The initial difference in position between the minute hand and the hour hand is: 120100=20120^\circ - 100^\circ = 20^\circ

Step 4: Time to meet

To find when they will meet, we calculate how long it will take for the 20-degree difference to be closed at the relative speed of 5.5 degrees per minute: Time=205.5/minute3.636 minutes\text{Time} = \frac{20^\circ}{5.5^\circ/\text{minute}} \approx 3.636 \text{ minutes}

Rounding to the nearest minute, the hour and minute hands will first meet in 4 minutes.

Conclusion

The hour and minute hands of the clock will first meet each other approximately 4 minutes from now.


Would you like further details on any part of this solution? Here are five related questions you might find interesting:

  1. How does the calculation change if the clock reads 4:45 AM instead of 3:20 AM?
  2. What would be the meeting time if the hands were exactly 180 degrees apart initially?
  3. Can you determine how many times the hour and minute hands meet within 12 hours?
  4. How do the speeds of the hour and minute hands compare over the course of a full day?
  5. What is the angle between the hands at 9:45 AM?

Tip: Understanding the relative speeds of clock hands can help solve many types of clock-related problems.

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Math Problem Analysis

Mathematical Concepts

Geometry
Trigonometry
Clock Arithmetic

Formulas

Angle calculation formulas for clock hands

Theorems

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Suitable Grade Level

Grades 9-12