On a map of England and Wales the distance between St Ives in Cornwall and St Ives in Cambridgeshire measures $$18\text{cm}$$. In reality the distance between the two towns is about $$450\text{km}$$.  Which of the options below is the scale of the map? 
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The scale of the map is $$18\text{cm} : 450\text{km}$$; converting the actual distance to centimetres, this is equivalent to $$18 : 450 \times 1000 \times 100 = 18 : 45 000 000$$. Simplifying gives a scale of $$1 : 2 500 000$$. 