Question 66139
{{{.1x + .35(400 - x) = .25*400}}}
{{{.1x + 140 - .35x = 100}}}
{{{-.25x = -40}}}
{{{x = 160}}}
{{{400 - x = 240}}}
You must mix 160 gallons of the 10% gasohol with 240 gallons 
of the 35% gasohol to get 400 gallons of the 25% gasohol
check
{{{.1x + .35(400 - x) = .25*400}}}
{{{.1*160 + .35*240 = 100}}}
{{{16 + 84 = 100}}}
{{{100 = 100}}}
OK