The supposition method solves word problems with two kinds of thing, a known number of things and a known total, but an unknown mix.
What your child learns here
The supposition method solves word problems with two kinds of thing, a known number of things and a known total, but an unknown mix. It applies the Primary 5 four operations of whole numbers to a classic problem sum, with a reason for each step.
Suppose every item is one kind and work out the total that would give.
Find the difference between the supposed total and the real total.
Find how much one swap changes the total: the difference in value between the two kinds.
Divide to find the number of swaps, which is the number of the other kind.
Say which kind has been counted before writing the answer.
Does the answer make sense?
When the question gives how many things there are and their total value, the count your child finds for one kind must be less than that number of things. If the real total sits nearer the all-higher-value total, more than half the things must be the higher-value kind.
How to practise these questions
Basic questions train the supposition method: imagine every item is one kind, then use the shortfall to count the other kind. Intermediate questions apply it to prices and to scores where marks are gained and lost. In the Challenge set the given figure is a gap or a net amount instead of a plain total, or a shortfall and a surplus must be compared, so the supposition needs careful setting up. If the method stalls, watch that question's solution film, then revisit it later from Revision.
Questions parents ask
What is the supposition method? It solves questions with two kinds of item and an unknown mix: suppose all are one kind, see how far the total is from the real one, and count the swaps needed to close the gap.
Is the supposition method in the Primary 5 syllabus? The syllabus lists the four operations of whole numbers, not named methods. Supposition is one way of using them in word problems, and this page teaches it step by step.
Can these questions be solved with a table instead? Yes, guess and check in a table also works, but it can take many rows. Supposition reaches the answer in a few lines of working.
