©
Wendy Fortescue-Hubbard and H G Beere
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Envelopes contain things
Envelopes contain things, but we do not know what is in them until we open them. Envelopes are also called letters, which is useful because in algebra, mathematicians use letters to represent numbers, and we don't always know what in the letter; that is, how much the letter is worth. This is because the letters mathematicans use are variable - they can mean any number.
Sometimes, though, the letter the mathematician uses is set to be equal to some number, and this lets us work out how much the letter is worth.
In this program all the letters contain matchsticks. You have to work out how many matchsticks there are in each letter.
There is a balance, and there are envelopes and/or matchsticks on the balance. At the start both sides are in balance; that is, one side is equal to the other (the envelopes on this balance have no mass, but the matchsticks they contain do).
You can take away matchsticks or envelopes, or add them, to work out how many matchsticks there are in each envelope.
Although the number of matchsticks varies from round to round, each envelope will contain the same number of matchsticks.
There are four levels of difficulty.