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Using the towns shown in Fig. 7.1, town B is $36\text{ km}$ east and $15\text{ km}$ north of town A. What is the distance between A and B? 
A$39\text{ km}$
B$41\text{ km}$
C$45\text{ km}$
D$51\text{ km}$
Answer & Solution
Correct answer: A. $39\text{ km}$
The east-west and north-south displacements form a right triangle. So, by Pythagoras theorem, $AB=\sqrt{36^2+15^2}=\sqrt{1296+225}=\sqrt{1521}=39\text{ km}$.
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