Convert seconds to minutes.
Subtract minutes and seconds using a 24-hour clock
Devise and use problem solving strategies to explore situations mathematically (be systematic).
First the students have to know that there are 31 days in May, 60 minutes in an hour and 60 seconds in a minute. Then they have to realise that Moana’s watch will be showing less than 13:00:00. Hence they have to find out how much the watch has lost in 31 days and subtract that from 13:00:00.
Moana set her digital watch at 13:00:00 on the last day of April. Unfortunately the watch loses 11 seconds a day. What is the time on Moana’s watch when it is 13:00:00 on the last day of May?
- Pose the problem. To capture the interest of the students you could personalise the problem by showing a digital watch and saying that it loses 11 seconds a day.
- Check that the calendar is displayed so that the students can find out how many days there are in May.
- As the students work on the problem ask questions that focus their thinking on the calculations that they are using.
How did you work out the number of seconds the watch had lost?
Does your final answer seem reasonable? Why? How could you check?
- Encourage the students to record their solutions for display at the end of the class.
- Share solutions.
Extension to the problem
What if the watch lost 11 seconds an hour. What would the time read on Moana's watch?
Solution to the problem
Since there are 31 days between the last day of April and the last day of May, Moana’s watch will have lost 31 x 11 = 341 seconds. To convert this into minutes, divide by 60. Hence 341 seconds = 5 minutes and 41 seconds. We now have to subtract 5 minutes 41 seconds from 13:00:00. This gives 12:54:19. This is the time on Moana’s watch.