Moana's watch

Achievement Objectives
GM4-1: Use appropriate scales, devices, and metric units for length, area, volume and capacity, weight (mass), temperature, angle, and time.
Student Activity

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?

Specific Learning Outcomes
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).
Description of Mathematics

To solve this problem students must know the number of days in each month, that there are 60 minutes in an hour, and 60 seconds in a minute, and must be able to work between units of time.

Required Resource Materials
Activity

Problem

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?

Teaching sequence

1. Pose the problem. Have students suggest adjustments they would need to make if their own watches lost 11 seconds each day.
2. Confirm the number of days in May.
3. 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?
4. Encourage the students to record their solutions for display at the end of the class.
5. 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. Then subtract 5 minutes 41 seconds from 13:00:00. This gives 12:54:19. This is the time on Moana’s watch.

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