The time Shaz takes to run a race is 1 minute 28 seconds less than 2 hours. Work out her time in hours, minutes and seconds.
How to approach this question
1. Start with the initial time: 2 hours, 0 minutes, 0 seconds.
2. You need to subtract 1 minute and 28 seconds.
3. It's easier to work backwards from the seconds. We can't subtract 28 seconds from 0 seconds, so we need to borrow from the minutes.
4. Borrow 1 minute from the 0 minutes. To do this, first borrow 1 hour from the 2 hours.
5. 2 hours 0 minutes becomes 1 hour 60 minutes.
6. Now borrow 1 minute from the 60 minutes.
7. 1 hour 60 minutes 0 seconds becomes 1 hour 59 minutes 60 seconds.
8. Now perform the subtraction:
1h 59m 60s
- 0h 01m 28s
-----------------
9. Seconds: 60 - 28 = 32 seconds.
10. Minutes: 59 - 1 = 58 minutes.
11. Hours: 1 - 0 = 1 hour.
12. The final time is 1 hour, 58 minutes, 32 seconds.
Full Answer
We need to calculate 2 hours minus 1 minute 28 seconds.
Method 1: Subtraction with borrowing
We can set up the subtraction like this:
2h 00m 00s
- 0h 01m 28s
We can't subtract 28 from 0, so we need to borrow.
Borrow 1 minute from the minutes column, which gives us 60 seconds. But we have 0 minutes, so we must first borrow from the hours column.
2 hours becomes 1 hour and 60 minutes.
So we have:
1h 60m 00s
- 0h 01m 28s
Now we can borrow 1 minute from the 60 minutes, leaving 59 minutes and giving us 60 seconds.
1h 59m 60s
- 0h 01m 28s
------------------
1h 58m 32s
So the time is 1 hour, 58 minutes, and 32 seconds.
Method 2: Using seconds
2 hours = 2 * 3600 = 7200 seconds.
1 minute 28 seconds = 60 + 28 = 88 seconds.
Time taken = 7200 - 88 = 7112 seconds.
Now convert back:
7112 / 3600 = 1 with a remainder of 3512. So, 1 hour.
3512 / 60 = 58 with a remainder of 32. So, 58 minutes.
Remainder is 32 seconds.
Answer: 1 hour 58 minutes 32 seconds.
Common mistakes
✗ Incorrectly borrowing time (e.g., thinking 1 minute = 100 seconds).
✗ Subtracting minutes from hours directly.
✗ Calculation errors in subtraction.
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