Decimal time
Use the clocks to investigate French decimal time in this problem.
Can you see how this time system worked?
Age
11 to 14
Challenge level
Problem
In France in 1793 decimal time was introduced, then abandoned only two years later.
Look at these pairs of times. The one on the left is our time and the clock on the right shows the corresponding French decimal time.
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Can you decipher how French decimal time works?
How did you use the clocks to help you?
Click here for a poster of this problem.
Getting Started
What does the word "decimal" make you think of? You could try looking it up in a dictionary.
How many hours are there in one of our days? What time is it half way through our day?
So, what time is it half way through the French decimal day? What does this tell you about the total number of hours in the French decimal day?
Do both systems have the same number of minutes in an hour?
How many hours are there in one of our days? What time is it half way through our day?
So, what time is it half way through the French decimal day? What does this tell you about the total number of hours in the French decimal day?
Do both systems have the same number of minutes in an hour?
Student Solutions
Congratulations to all of you who correctly gave the solution to this problem. There are too many of you to list here.
Harry of CPS was the first to send in a correct answer.
In decimal time the time only goes up to 10 so halfway through our day it is 12.00 and halfway through their day it is 5.00
A team from Oatlands Junior School went on to explain why 15:43 our time is 6:54 French Decimal Time.
In one UK day there are 24 hours, but for the French time there are 10 units of time.
And also for 1440 minutes the French equivalent would be 1000 French mins.
1 minute (English)= 1000 minutes (French)/ 1440 which was 0.6944.
They go on to work out how many minutes past midday (5:00 French Decimal Time) is equivalent to 15:43
The English clock moved 3hrs 43mins (223 minutes) We multiplied 0.6944 by 223 mins to get the French equivalent which was 154.86 French minutes. So the French clock moved 154.86 French minutes to get to 6:54.
Teachers' Resources
This problem is designed to intrigue a little. To tackle the problem, pupils will need to be comfortable with manipulating fractions and decimals, and it would be a good idea to have calculators to hand.
It is an excellent way to highlight misconceptions associated with our digital clock, for example that 12.50 is not 0.5 hours after 12.00. It could be a good vehicle for investigating why our clock is based on the number 60 and researching calendar systems of ancient cultures.