Question 1184802
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For x + u = N, the maximum product xy is {{{(N/2)^2}}}

So  {{{ (16.8/2)^2 }}} will be the max product.

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Derivation:
x + y = N --->  y = N-x

Now product p is:
{{{ p = xy = x(N-x) = Nx - x^2 }}}

{{{ dp/dx = N-2x }}}
{{{ N-2x = 0 }}}  --->  x = N/2  

This is a local MAX value b/c {{{ d^2p/dx^2 = -2 }}} which is concave DOWN.