Question

An accurate clock indicates 9'O clock in the morning. Through how many degrees the hour hand turns when the clock indicates 4'O clock in the afternoon?

• A. 180 degree
• B. 210 degree
• C. 280 degree
• D. 320 degree

Hint:

Memorize the speeds of the clock hands:

\textbf{Hour Hand:} 0.5 degrees per minute (or 30 degrees per hour).
\textbf{Minute Hand:} 6 degrees per minute.
These values are fundamental for solving almost any clock-related problem.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
We need to calculate the total angle moved by the hour hand of a clock from 9:00 AM to 4:00 PM.

Step 2: Key Formula or Approach


The hour hand completes a full circle (360°) in 12 hours.
Speed of the hour hand = \( \frac{360^\circ}{12 \text{ hours}} = 30^\circ \) per hour.
Speed of the hour hand = \( \frac{30^\circ}{60 \text{ minutes}} = 0.5^\circ \) per minute.

Step 3: Detailed Explanation
1. Calculate the total time elapsed:
The time is from 9:00 AM to 4:00 PM.
From 9:00 AM to 12:00 PM (noon) = 3 hours.
From 12:00 PM to 4:00 PM = 4 hours.
Total time = 3 + 4 = 7 hours.
2. Calculate the total angle moved:
The hour hand moves at a speed of 30° per hour.
Total angle = (Speed of hour hand) \(\times\) (Total time in hours)
\[ \text{Total angle} = 30^\circ/\text{hour} \times 7 \text{ hours} \] \[ \text{Total angle} = 210^\circ \]
Step 4: Final Answer
The hour hand turns through 210 degrees from 9:00 AM to 4:00 PM. Therefore, option (B) is the correct answer.