There are 9 different rock lizard species, each with a unique colour. Lizards of 2 different species sit on a rock at any given time. The number of possible colour combinations of rock lizards seen together on a rock is:
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Solution and Explanation
The problem asks for the number of combinations where we pick 2 different species from a group of 9. The combination formula is: \[ \binom{9}{2} = \frac{9 \times 8}{2} = 36 \] Step 2: Conclusion Thus, the number of possible colour combinations of rock lizards is \( \boxed{36} \).
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