Zachary arrived at the swimming club at 15:20. He took 42 minutes to travel from his house to the club. At what time did he leave his house?
Understand the Problem
The question asks to compute the time that Zachary left his house, given that he arrived at the swimming club at 15:20 and it took him 42 minutes to travel there.
Answer
14:38
Answer for screen readers
14:38
Steps to Solve
- Convert the arrival time to minutes
Convert 15:20 to minutes. There are 60 minutes in an hour, so 15 hours is $15 \times 60 = 900$ minutes. Adding the 20 minutes gives a total of $900 + 20 = 920$ minutes.
- Subtract the travel time
Subtract the travel time of 42 minutes from the arrival time in minutes: $920 - 42 = 878$ minutes
- Convert back to hours and minutes
Convert 878 minutes back into hours and minutes. Divide 878 by 60 to find the number of hours: $878 \div 60 = 14$ with a remainder of 38. This means the time is 14 hours and 38 minutes, or 14:38.
14:38
More Information
The 24-hour clock is commonly used to avoid confusion between AM and PM.
Tips
A common mistake is to subtract the minutes incorrectly, especially when the number of minutes to subtract is larger than the number of minutes in the arrival time. For example, if the arrival time was 15:10 and the travel time was 20 minutes, subtracting 20 from 10 directly would lead to a negative number. In such cases, one needs to borrow an hour (60 minutes) from the hours place before subtracting.
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