Stage: 2 Challenge Level: 
On the planet Vuv there are two sorts of creatures. The Zios have $3$ legs and the Zepts have $7$ legs.
The great planetary explorer Nico, who first discovered the planet, saw a crowd of Zios and Zepts. He managed to see that there was more than one of each kind of creature before they saw him. Suddenly they all rolled over onto their backs and put their legs in the air.
He counted $52$ legs. How many Zios and how many Zepts were there?
Working systematically. Multiplication & division. Divisibility. Combinations. Factors and multiples. Generalising. Trial and improvement. Addition & subtraction. Interactivities. Investigations.
Published June 2000,January 2009.
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