Question 107859
Draw the picture:
You go 50 km West, then 20 km North.  How many km are you from where you started?
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The picture shows you have two sides of a right angle.
Connect the beginning point to the point where you end up; 
that is the distance you need to determine.
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Using Pythagoras:
hypotenuse^2 = 50^2 + 20^2
h^2 = 2500 + 400
h^2 = 2900
h = sqrt(2900)
h = 10sqrt(29) which is approximately 53.85 km
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Cheers,
Stan H.