Question

7. Elle can buy milk at a local farmers'
market for $3.58 per gallon or at the
grocery store for $3.79 for 4 L. Which
is the better buy?

Answer 1

Answer:  They are the same equivalent price, $0.95/liter.

Step-by-step explanation:

Choices:  $3.58 per gallon, or $3.79 for 4 L.

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We need to convert one of the volumes.  I'll convert gallons to liters.

By definition, 1 gallon = 3.785 liters

Make this into a conversion factor:

We can make it either:

1)   (3.785 liters/gallon), or

2)  (1 gallon/3.785 liters)

Now convert the $3.58/gallon into dollars/liter.  We'll use the second conversion factor so that gallons cancels out when we multiply:

($3.58/gallon)*(1 gallon/3.785 liters) = $0.95/liter.

The grocery store milk must also be converted to a price expressed per 1 liter:

$3.79 for 4 L

= $0.95/liter.

They are the same equivalent price, $0.95/liter.