Clock Arithmetic

Goals

• Learn what clock arithmetic is

• Practice clock arithmetic

• Investigate the rules for using clock arithmetic

What To Do

• 1. Explain the concept of clock arithmetic

  2. I start with a real clock size but quickly move to a clock of 5 to make the calculations easier.

  3. Provide a list of sums to be practice on

     1. Initially students can count round the clock

     2. Student can look for shortcuts to bypass the counting

  4. For a two number sum, first simplify each number to the 'remainder' and then add these remainders. Does this give the same answer as for 3)?

  5. Give the student large sums to challenge to find a solution without counting.

  6. Optional: Talk about the trick for calculating whether a number is divisible by three and prove this using clock arithmetic.

Homework

• Complete the problem list for a clock of size 3

  • Remember the trick for calculating whether a number is divisible by 3.