Question 23246
Set up a ratio of gas to total fuel.  8 parts gas + 2 parts oil = 10 parts total fuel.


Let x = number of gallons of gas needed to make 20 gallons of fuel.
{{{(gas)/(total) = 8/10= x/20}}}


Remember {{{a/b=c/d}}} means that {{{ad=bc}}}


In the same way, {{{8/10= x/20}}} means that {{{8*20=10*x}}}

10x = 160
x= 16 gallons


You can do it in your head without an equation if you like.  Just think about the ratio of 8 gallons of gas to 10 gallons total.  The 20 gallons total is exactly twice as much as the 10 gallons, so the gas will be exactly twice the 8 gallons or 16 gallons.  However, it usually doesn't work out this nicely.  That's why I like to do it with the ratio and equation.


R^2 at SCC