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Problem of the Week

Ku-ring-gai Postcodes

Ku-ring-gai is a local government area in Northern Sydney.

From this image, could you determine the number of different postcodes in Ku-ring-gai?

Are postcodes cardinal, ordinal or nominal numbers?


Cardinal numbers are the numbers that are used for counting.

Ordinal numbers are numbers that indicate the order or rank of things.

Nominal numbers are numbers used for the purpose of identification.


Postcodes are used to identify different areas, so they are nominal numbers.

For example, the postcode 2073 does not mean that there are 2 thousand and 73 of anything (cardinal) or that the area is 2 thousand and 37th in some order (ordinal).

2073 is just a label used to identify an area.


Because the numbers are nominal, we cannot assume that the consecutive postcodes from 2069 to 2076 are in Ku-ring-gai and no other postcode is within this local government area.

However, the data below which comes from the website: https://aus.postcodebase.com/region3/ku-ring-gaist-leonards

shows that these postcodes are all in Ku-ring-gai and no other postcode is in Ku-ring-gai.

The postcodes are consecutive and are in the range of 2069 to 2076.

Therefore, the number of postcodes in Ku-ring-gai is:

2076 – 2069 + 1 = 8. (One is added because we are finding the difference between 2 numbers where the first number is included in the count.)

The 8 postcodes are: 2069, 2070, 2071, 2072, 2073, 2074, 2075 & 2076




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