what's the chance of seeing 4 double-digits on a mobile phone's digital clock during a 17hr waking period between 07:07 & 23:23hrs; eg. 07:07, 16:16, 23:23.

1 answer

To determine the chance of seeing double-digit times on a digital clock within the 17-hour period from 07:07 to 23:23, we start by identifying all the possible times that meet the double-digit criteria during this window:

Definitions:

  • Double-digit time: Times where the hour and minute each are at least 10 (i.e., for hours 10:00-23:59, but with the additional restriction of being within the bounds of 07:07 and 23:23).

Double-digit Analysis:

In a 24-hour format, the times with double-digit hours that we can consider are:

  • 10:00 to 10:59
  • 11:00 to 11:59
  • 12:00 to 12:59
  • 13:00 to 13:59
  • 14:00 to 14:59
  • 15:00 to 15:59
  • 16:00 to 16:59
  • 17:00 to 17:59
  • 18:00 to 18:59
  • 19:00 to 19:59
  • 20:00 to 20:59
  • 21:00 to 21:59
  • 22:00 to 22:59
  • 23:00 to 23:23 (restricting minutes to the first 23 minutes)

Range of Double-Digit Times:

  • 10:00 to 10:59: 60 minutes
  • 11:00 to 11:59: 60 minutes
  • 12:00 to 12:59: 60 minutes
  • 13:00 to 13:59: 60 minutes
  • 14:00 to 14:59: 60 minutes
  • 15:00 to 15:59: 60 minutes
  • 16:00 to 16:59: 60 minutes
  • 17:00 to 17:59: 60 minutes
  • 18:00 to 18:59: 60 minutes
  • 19:00 to 19:59: 60 minutes
  • 20:00 to 20:59: 60 minutes
  • 21:00 to 21:59: 60 minutes
  • 22:00 to 22:59: 60 minutes
  • 23:00 to 23:23: 24 minutes

Total Double-Digit Minutes:

Calculating the total minutes for the above:

  • From 10:00 to 22:59: 13 hours × 60 minutes = 780 minutes
  • From 23:00 to 23:23: 24 minutes

Total double-digit minutes = 780 + 24 = 804 minutes.

Total Waking Minutes:

The total time from 07:07 to 23:23 is:

  • 23:23 - 07:07 = 16 hours and 16 minutes.
  • 16 hours = 960 minutes + 16 minutes = 976 minutes.

Probability:

If we want to find the probability of seeing a double-digit time in that window, we now set up the expression.

  • Total possible moments to see the clock = 976 minutes.
  • Favorable moments to see a double-digit time = 804 minutes.

Calculating the probability: \[ \text{Probability} = \frac{\text{Favorable Outcomes}}{\text{Possible Outcomes}} = \frac{804}{976} \approx 0.821, \text{ or } 82.1% \]

Conclusion:

Thus, the chance of seeing double-digit times on a mobile phone's digital clock during the specified period is approximately 82.1%.