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These puzzles help develop understanding of the association between different operations. There are several approaches to solving these puzzles. The simplest is to look at the numbers given in the addition and subtraction sums. Half-way between these numbers will always give you the value *. In puzzle 1 half-way between 5 and 15 is 10. Equally half the difference between these two given numbers must also be the value ?. E.g. 10 - 5 = 5 or 15 -10 = 5. Use the multiplication and division sums to check. An alternative approach is to create a trial and error table for the multiplication and division sums. What happens when you multiply and divide by 1, or 2, then try 3 etc?