Aunt Sophie has 5p and 9p stamps only.
It will cost 91p to post a parcel.
How many of each type of stamp should she put on the parcel?
5p
9p
Aunt Ann visited the post office too.
She has many 4p and 9p stamps.
What's the largest whole number amount that can't be made with Aunt Ann's stamps?
4p
9p
Topics: Starter | Arithmetic | Investigations | Money | Number | Tables
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Click here for the Aunt Sophie answers
The answer to Aunt Ann's problem is 23p.
The solution to this type of problem for a given set of stamp values is called the Frobenius number of the set. The Frobenius number exists as long as the set of coin denominations has no common factor greater than 1.
The formula for the Frobenius number when there are only two different stamp values, x and y is: xy − x − y
Note to teacher: Doing this activity once with a class helps students develop strategies. It is only when they do this activity a second time that they will have the opportunity to practise those strategies. That is when the learning is consolidated. Click the button above to regenerate another version of this starter from random numbers.
Teacher, do your students have access to computers such as tablets, iPads or Laptops? This page was really designed for projection on a whiteboard but if you really want the students to have access to it here is a concise URL for a version of this page without the comments: Transum.org/go/?Start=July8 However it would be better to assign one of the student interactive activities below. |
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Here is the URL which will take them to an interactive stamp sticking activity.