A driver starts a trip with 30 gallons of gasoline in the tank of his car. The car
burns 4 gallons for every 80 miles. Assuming that the amount of gasoline in the tank decreases linearly, write a linear function that relates the number of gallons G left in the tank after a journey of "d" miles.

We have to look at this as something as basic as combining like terms. We know that the driver starts with 30 GALLONS of gas and loses x GALLONS while driving, giving us an equation that says

Gallons of gas used = Gallons in car - gallons used; in other words, if everything is in the same label, you can subtract. We start off with 30 gallons, thus:

Gallons of gas used = 30 G

That's a start, at least. Now we need to figure out how much is burned. Remember, in order to do any subtraction at all we have to have like labels, so we need what goes after that subtraction sign to also be a label in gallons, G. The driver burns 4 gallons per 80 miles times how many miles he drives, so the expression for that is

[tex]\frac{4G}{80mi}*dmi[/tex] and what happens here is that the label of miles cancels out, leaving us with just G, which is what we're after. The whole equation then is

[tex]G=30-\frac{4}{80}d[/tex], choice 1

A driver starts a trip with 30 gallons of gasoline in the tank of his car. The car burns 4 gallons for every 80 miles. Assuming that the amount of gasoline in the tank decreases linearly, write a linear function that relates the number of gallons G left in the tank after a journey of "d" miles.

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A driver starts a trip with 30 gallons of gasoline in the tank of his car. The car
burns 4 gallons for every 80 miles. Assuming that the amount of gasoline in the tank decreases linearly, write a linear function that relates the number of gallons G left in the tank after a journey of "d" miles.