How do you find the cost of a gallon of water if the cost of a gallon of milk is $.50 more than five times the cost of a gallon of water and if a gallon of milk costs $3.75?

A gallon of water costs 65 cents.

Now, you could set up an equation, or you could just talk it out. When you get really good, you'll see that those two methods are really one and the same. Equations are how mathematicians talk stuff out.

A gallon of milk is 50 cents more than 5 times a gallon of water, and we know that that's $3.75.

##$3.75 - $0.50 = $3.25##

So, you can get 5 gallons of water for $3.25. So to get one gallon, you just need one-fifth of $3.25.

##$3.25 -: 5 = $0.65##

And there's your 65 cent cost.

How do we set up an equation? Let w be the cost of a gallon of water.

$3.75 is 50 cents bigger than 5 times g. We can write that like this:

##3.75=5g + 0.50##

And we can solve for g.

##g=0.65##, which is 65 cents