Question 314801
1.{{{40X+70Y=50(24)}}}
2.{{{X+Y=24}}}
Multiply eq.  by -40 and add to eq. 1,
{{{40X+70Y-40X-40Y=1200-960}}}
{{{30Y=240}}}
{{{Y=8}}}
Then from eq. 2,
{{{X+8=24}}}
{{{X=16}}}
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16 gallons of 40% solution and 8 gallons of 70% solution.