A clock is 5 minutes fast at 10:00 AM and 15 minutes fast at 4:00 PM. At what time (in AM) will it show the correct time?
Show answer & explanation
Correct answer: A
Explanation
Hourly Rate of Gaining:
In 6 hours, the clock gained 10 minutes. Therefore, the rate at which the clock gains per hour is: 10 minutes / 6 hours = 5/3 minutes per hour.
Correct Time (0 minutes gain):
At 10:00 AM, the clock was already 5 minutes fast. This implies that the point at which it showed the 'correct time' must have occurred prior to 10:00 AM.
We need to determine how long it took for the clock to gain 5 minutes.
Time taken =
Since the clock was 5 minutes fast at 10:00 AM, it must have shown the correct time 3 hours earlier.
Correct Time = 10:00 AM - 3 hours = 7:00 AM.
Conclusion:
The clock was showing the correct time at 7:00 AM.