Sooner or later, all math leads to Calculus, no matter how much we would like to beleive that isn't true. Here's our Calc section... Brush up on your college math, pull out a your dusty textbook and get comfy.
Johnny left point A, walking North at a steady velocity V km/h . At the moment that he was at a distance of 6 km from A, a biker Tom left A to bring Johnny back, his speed being 9 km/h higher than Johnny's.
When they met they turned back and travelled South at 4 km/h.
For what value of V the duration of Johnny's trip would be minimal?
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