We have looked at situations in which we need to determine the number of possible routes between two places. We can look at the situation below as 9 steps, six of which must be East and three of which must be South.

This gives us

possible routes.

The calculation

is equivalent to ₉C₃ (or ₉C₆).

Explain clearly why you could solve this question using combinations, and why this is equivalent to considering permutations with repeated items.

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