Change in Thinking

Activity One

This activity contrasts two methods for calculating change: adding on and subtracting. Generally, the adding-on method works best with small sums of money, but it is not always easy to use when large numbers are involved.
Students will have their own variations based on these main strategies. For example:
“A $1 price would mean $1 change. A $1.50 price would mean 50 cents change. $1.25 is between the two, so that means 75 cents change.”
“It’s like paying for something that costs 25 cents with a $1 coin. Four lots of 25 cents make $1. That leaves three lots of 25 cents, which is 75 cents.”

Activity Two

In attempting this activity, students may find that their preferred strategy changes, depending on the example. Students usually prefer adding on when this can be done easily. For example, paying for a $2.70 drink with two $2 coins:

Answers to Activity

Activity One
Answers will vary.
Mr Patel might say his calculation out loud as he hands over the money so you can be sure you’ve got the right change. However, it may take longer than Mrs Grey’s
method.
Activity Two
Ice cream: 80c change
Chocolate bars: $1.30 change
Diary: $4.50 change
Pad and notebook: 90c change
Zinc: 15c change.