Question 1155527
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two brothers leave their house at the same time. alex runs due east at a constant speed of 10km per hour, 
and Boris walks due south at a constant speed of 4km per hour. How far has each brother travelled after 30 minutes?
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Regarding the solution in the post by @mananth, I'd like to notice that the problem
does not require to calculate the distance between the brothers after 30 minutes.


So, this calculation is unnecessary and performed by @mananth without any real necessity.