hand sanitizer

Jason has 4 gallons of hand sanitizer that contains 25% alcohol. He wants to make a hand sanitizer that contains 50% alcohol. How many gallons of pure alcohol should he add?

Hello Guest!

$4\ gal\cdot 25\%+x=(4\ gal+x)\cdot 50\%\\ 4\ gal\cdot 0.25+x=4\ gal\cdot 0.5+x\cdot 0.5\\ 0.5x=4gal\cdot (0.5-0.25)$

$x=\dfrac{4\cdot 0.25}{0.5}gal$

$x=2\ gal$

Jason should add 2 gallons of pure alcohol.

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