Question 844196
Maybe a mixture problem but also a linear system problem.


n is how many new
p is how many previous versions


Account for total versions sold:  {{{n+p=15}}}
Account for sales value:  {{{60n+40p=840}}} which is simplifiable to {{{3n+2p=42}}}


SOLVE THE SYSTEM:
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n+p=15
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3n+2p=42
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Choosing Elimination Method, you can use 2n+2p=30 and 3n+2p=42, and subtract first equation from second equation.
{{{(3n+2p)-(2n+2p)=42-30}}}
{{{3n+2p-2n-2p=12}}}
{{{n+0=12}}}
{{{highlight(n=12)}}} and this means {{{highlight(p=3)}}}