Cracked Clock

A clock broke into two pieces.
The numbers on each of the pieces add up to the same total.


Draw a diagram to show how the clock cracked.

A Mathematics Lesson Starter Of The Day


Topics: Starter | Arithmetic | Problem Solving

  • Ruth Seward, Hagley Park Sports College
  • Find the starters wonderful; students enjoy them and often want to use the idea generated by the starter in other parts of the lesson. Keep up the good work
  • Y8 set 1 Rawthorpe High School, The Cushtie Krew
  • We think that this was very good. We liked the clock, in fact we thought it was a cracking starter!
    Maths rules, Cushtie!
  • Sue, St Albans
  • The question can be extended to 'the clock is broken into three pieces with equal sum of 26 -- piece one contains numbers 11, 12, 1, and 2; piece two contains 3, 4, 9, & 10; the rest is piece three'.
    Equally, it can be broken into 6 pieces with an equal sum of 13 -- piece one has 12 and 1; piece two has 2 and 11; piece three 3 and 10.
  • Russ Skinner, Winnipeg, MB
  • This problem also works by breaking the clock into 3 pieces and 6 pieces. The sum of all the numbers around the clock (1 + 2 + 3...10 + 11 + 12) equals 78. 78 is divisible by 3 and 6.
  • The Best Class Ever (8cd/m2), King Alfred's College OXON
  • We decided that this starter was not explained enough to work it out, so we tried both ways we could thing of and then realised that they were both the same answer.Tash, Ryan and Liam worked this out straight away with others not far behind them.
  • Kieran, Weston
  • I found this easy to understand, and once I found pairs of 13 it was easy.

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This starter has scored a mean of 3.2 out of 5 based on 476 votes.

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Have you read Craig's book yet?

Craig Barton must surely be the voice of Mathematics teachers in the UK. His wonderful podcasts interviewing the industry experts have culminated in this wonderful book. As Craig says: "I genuinely believe I have never taught mathematics better, and my students have never learned more. I just wish I had known all of this twelve years ago..." more...

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Laptops In Lessons

Teacher, do your students have access to computers?
Do they have iPads or Laptops in Lessons?

Whether your students each have a TabletPC, a Surface or a Mac, this activity lends itself to eLearning (Engaged Learning).

Laptops In Lessons

Here a concise URL for a version of this page without the comments.

Here is the URL which will take them to a related student activity.

Student Activity




Clock 1 Clock 2 Clock 3

Which clockface is the odd one out?

The answer can be found by looking closely at the roman numerals used.





Extension Answer

The clock on the right uses IIII for the number 4 while the other two clocks use IV.

Investigate which system of numbers is most common on clocks in your school, home or place of work.



More questions:

There are more questions like these on the interactive Clock page.


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