Eric C. answered • 07/19/16

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Engineer, Surfer Dude, Football Player, USC Alum, Math Aficionado

Hi LEX.

This is a system of equations question in disguise. As with every system of equations question, it's best to call/ define some variables.

I'm going to say that:

A = the COST of a gallon of anti-freeze

W = the COST of a gallon of water

Note that I defined the variables not as the amount of fluid, but the cost of each fluid.

From the information given we can write two equations. The first being:

A = 12.99

This is stating that the cost of a gallon of anti freeze is 12.99.

The second equation is a bit more tricky to put together. You essentially have half a gallon of water and half a gallon of anti-freeze. You know that this totals $10.99. So you can state that:

A*1/2 + W*1/2 = 10.99

This is saying that the cost of half a gallon of antifreeze (A*1/2) PLUS the cost of half a gallon of water (W*1/2) EQUALS 10.99.

From the first equation we can substitute a real value in for A.

12.99*1/2 + W*1/2 = 10.99

This is now 1 equation, 1 unknown, and is entirely solvable.

6.495 + W/2 = 10.99

W/2 = 4.495

W = 8.99

From the definition of our variables above, this equation is saying the cost of the gallon of water is $8.99.

Tap water from your sink is a less than a penny per gallon. I think in California it's about 1/5 of a cent, meaning 5 gallons of water will cost you a penny. Best just to buy the pure anti-freeze and dilute it at home.

Hope this helps.

Sam C.

12/21/17