# Baker's dozen

Purpose

The purpose of this activity is to engage students in generalising the difference between two sequential counting numbers, in context.

Achievement Objectives
NA1-5: Generalise that the next counting number gives the result of adding one object to a set and that counting the number of objects in a set tells how many.
Description of Mathematics

In readiness for this problem, the students should have familiarity with each of the following components of mathematics. The problem may be solved with different combinations of these components.

• apply counting-all strategies
• continue sequential patterns and number patterns based on 1s
• know the result of adding 1 to a given counting number
• Compare two sequential counting numbers to find the difference

This activity may be carried out with guidance, or by allowing the student to follow their own set of instructions. The approach should be chosen in sympathy with students’ skills and depth of understanding.

Activity

A bag of‘a dozen’ donuts has 12 donuts in it.

If the bag is labelled ‘a baker’s dozen’ then it has 13 in it.

Explain the difference between a dozen and a baker’s dozen.