Question:medium

A clock is set right at 6 a.m. It gains 2 minutes every hour. What will be the true time when the clock shows 10 p.m. on the same day?

Show Hint

For clocks gaining time, calculate total gain over the period and subtract from the displayed time to find the true time.
Updated On: Jan 16, 2026
  • 9:36 p.m.
  • 9:28 p.m.
  • 9:48 p.m.
  • 10:00 p.m.
Show Solution

The Correct Option is B

Solution and Explanation

To determine the actual time when the clock indicates 10 p.m., considering it gains 2 minutes every hour from its setting at 6 a.m.

1. Foundational Principles:

- Initial Setting: 6 a.m.
- Rate of Gain: 2 minutes per hour.
- Observed Time: 10 p.m.
- Actual Time: The real elapsed time when the malfunctioning clock displays 10 p.m.

2. Provided Data:

- The clock advances by 2 minutes each hour.
- The duration recorded by the faulty clock from 6 a.m. to 10 p.m. is 16 hours.

3. Calculation of Elapsed True Time:

For every hour of true time, the clock advances by \( 60 + 2 = 62 \) minutes.

Let \( t \) represent the true elapsed time in hours.
The time displayed by the clock after \( t \) hours is calculated as:

\( \text{Clock Display} = \frac{62}{60} \times t = \frac{31}{30} t \)

Given that the clock displays 16 hours (from 6 a.m. to 10 p.m.):

\[ \frac{31}{30} t = 16 \]

Solving for \( t \):

\[ t = \frac{16 \times 30}{31} = \frac{480}{31} \approx 15.48 \text{ hours} \]

4. Conversion of True Time to Hours and Minutes:

The fractional part of the hours is 0.48 hours, which converts to minutes as:

0.48 hours =\( 0.48 \times 60 = 28.8 \text{ minutes} \), approximating to 29 minutes.

More precisely, \( \frac{480}{31} \) hours is equivalent to:

Full Hours = 15 hours
Remaining Minutes = \( \frac{480}{31} - 15 = \frac{480 - 465}{31} = \frac{15}{31} \) hours

Converting these remaining hours to minutes:

\( \frac{15}{31} \times 60 \approx 29.03 \) minutes. This value is closer to 29 minutes. For exact calculation, the minutes are 28.8, which translates to 28 minutes and 48 seconds.

5. Determination of Actual Time:

Starting from the set time of 6 a.m., adding the calculated true elapsed time of approximately 15 hours and 28 minutes yields:

6:00 a.m. + 15 hours 28 minutes = 9:28 p.m. (after accounting for the 12-hour cycle).

Final Conclusion:

The actual time when the clock shows 10 p.m. is approximately 9:28 p.m.

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